UserEventAgent won't let me eject my external hard drive, and other problems

Question

I'm running a MacBook Pro (2008-ish model) running Mountain Lion 10.8.2 with 4Gb of RAM and 750Gb of internal HD (the original 250Gb seriously cramped my style), and UserEventAgent is acting all weird.
Because of that old 250Gb HD, I was in the habit of storing files I didn't need at the time on an external hard drive, a LaCie 500Gb connected by FW800 (probably not relevant). And lately, whenever I plug it in, I can't eject it without forcing it to eject.
Using the "list open files" command and searching for that drive [ lsof | grep LaCie ] reveals that UserEvent drops an immediate hook in it for some reason. This connection is immediate, and short of force-quitting UserEventAgent in Activity Monitor at the exact moment I try to eject that drive, I can't disconnect it properly without forcing it or shutting down completely.
In fact, looking at UserEventAgent's open files and ports in Activity Monitor, something just plain doesn't look right:
/usr/libexec/UserEventAgent
/System/Library/Frameworks/Security.framework/PlugIns/csparser.bundle/Contents/M acOS/csparser
/private/var/folders/td/hnt8krzc8xj63p001s61rg7r0000gn/C/mds/mdsDirectory.db
/usr/share/icu/icudt49l.dat
/System/Library/UserEventPlugins/ACRRDaemon.plugin/Contents/MacOS/ACRRDaemon
/System/Library/KerberosPlugins/KerberosFrameworkPlugins/heimdalodpac.bundle/Con tents/MacOS/heimdalodpac
/System/Library/KerberosPlugins/KerberosFrameworkPlugins/LKDCLocate.bundle/Conte nts/MacOS/LKDCLocate
/System/Library/KerberosPlugins/KerberosFrameworkPlugins/Reachability.bundle/Con tents/MacOS/Reachability
/System/Library/KerberosPlugins/KerberosFrameworkPlugins/SCKerberosConfig.bundle /Contents/MacOS/SCKerberosConfig
/System/Library/UserEventPlugins/AirPortUserAgent.plugin/Contents/MacOS/AirPortU serAgent
/System/Library/UserEventPlugins/AppleHIDMouseAgent.plugin/Contents/MacOS/AppleH IDMouseAgent
/private/var/db/mds/messages/se_SecurityMessages
/System/Library/UserEventPlugins/AssistantUEA.plugin/Contents/MacOS/AssistantUEA
/System/Library/UserEventPlugins/AutoTimeZone.plugin/Contents/MacOS/AutoTimeZone
/System/Library/UserEventPlugins/BTMMPortInUseAgent.plugin/Contents/MacOS/BTMMPo rtInUseAgent
/System/Library/UserEventPlugins/BluetoothUserAgent-Plugin.plugin/Contents/MacOS /BluetoothUserAgent-Plugin
/System/Library/Extensions/AppleHDA.kext/Contents/PlugIns/AppleHDAHALPlugIn.bund le/Contents/MacOS/AppleHDAHALPlugIn
/System/Library/UserEventPlugins/BonjourEvents.plugin/Contents/MacOS/BonjourEven ts
/System/Library/UserEventPlugins/CalendarMonitor.plugin/Contents/MacOS/CalendarM onitor
/System/Library/UserEventPlugins/CaptiveUserAgent.plugin/Contents/MacOS/CaptiveU serAgent
/System/Library/UserEventPlugins/DiskUnmountWatcher.plugin/Contents/MacOS/DiskUn mountWatcher
/System/Library/UserEventPlugins/EAPOLMonitor.plugin/Contents/MacOS/EAPOLMonitor
/System/Library/UserEventPlugins/GSSNotificationForwarder.plugin/Contents/MacOS/ GSSNotificationForwarder
/System/Library/UserEventPlugins/LocationMenu.plugin/Contents/MacOS/LocationMenu
/System/Library/UserEventPlugins/PrinterMonitor.plugin/Contents/MacOS/PrinterMon itor
/System/Library/UserEventPlugins/SCMonitor.plugin/Contents/MacOS/SCMonitor
/System/Library/UserEventPlugins/alfUIplugin.plugin/Contents/MacOS/alfUIplugin
/System/Library/UserEventPlugins/com.apple.SoftwareUpdate.UserNotification.plugi n/Contents/MacOS/com.apple.SoftwareUpdate.UserNotification
/System/Library/UserEventPlugins/com.apple.TimeMachine.plugin/Contents/MacOS/com .apple.TimeMachine
/System/Library/UserEventPlugins/com.apple.bonjour.plugin/Contents/MacOS/com.app le.bonjour
/System/Library/UserEventPlugins/com.apple.cfnotification.plugin/Contents/MacOS/ com.apple.cfnotification
/System/Library/UserEventPlugins/com.apple.dispatch.vfs.plugin/Contents/MacOS/co m.apple.dispatch.vfs
/System/Library/UserEventPlugins/com.apple.fsevents.matching.plugin/Contents/Mac OS/com.apple.fsevents.matching
/System/Library/UserEventPlugins/com.apple.iokit.matching.plugin/Contents/MacOS/ com.apple.iokit.matching
/System/Library/UserEventPlugins/com.apple.launchd.helper.plugin/Contents/MacOS/ com.apple.launchd.helper
/System/Library/UserEventPlugins/com.apple.locationd.events.plugin/Contents/MacO S/com.apple.locationd.events
/System/Library/UserEventPlugins/com.apple.notifyd.matching.plugin/Contents/MacO S/com.apple.notifyd.matching
/System/Library/UserEventPlugins/com.apple.rcdevent.matching.plugin/Contents/Mac OS/com.apple.rcdevent.matching
/System/Library/UserEventPlugins/com.apple.time.plugin/Contents/MacOS/com.apple. time
/System/Library/UserEventPlugins/com.apple.universalaccess.events.plugin/Content s/MacOS/com.apple.universalaccess.events
/System/Library/UserEventPlugins/com.apple.usernotificationcenter.matching.plugi n/Contents/MacOS/com.apple.usernotificationcenter.matching
/System/Library/Extensions/IOHIDFamily.kext/Contents/PlugIns/IOHIDLib.plugin/Con tents/MacOS/IOHIDLib
/private/var/folders/td/hnt8krzc8xj63p001s61rg7r0000gn/C/com.apple.LaunchService s-036501.csstore
/usr/lib/dyld
/private/var/db/dyld/dyld_shared_cache_x86_64
/dev/null
/dev/null
/dev/null
count=1, state=0x2
/dev/io8log
/Users/<username>/Library/Assistant/sync_flag
->0xc1a78b298c30c655
count=0, state=0
count=0, state=0
/private/etc/com.apple.screensharing.agent.launchd
/private/etc
/private
/usr/local/bin
/usr/local/bin
/usr/local
/usr
count=0, state=0
/private/var/db/PanicReporter
/private/var/db
/private/var
/private
count=0, state=0
/private/var/db/GPURestartReporter
/private/var/db
/private/var
/private
count=0, state=0
/private/etc
/private/etc
/private
count=0, state=0
/Users/<username>/Library/Services
/Users/<username>/Library
/Users/<username>
/Users
count=0, state=0
/Library
/Library
count=0, state=0
/Applications
/Applications/Utilities
/Applications
count=0, state=0
/Library/Caches
/Library/Caches
/Library
count=0, state=0
/Library/Preferences/com.apple.AirPortBaseStationAgent.launchd
/Library/Preferences
/Library
count=0, state=0
/Applications/Fun/Steam.app
/Applications/Fun
/Applications
/Volumes
/Volumes
The repetitions (I mean seriously, who needs three open connections to /dev/null?), and the multiple instances of "count=0, state=0", suggest that UserEventAgent is getting bad info from somewhere.
If I can track down what's making UserEventAgent imitate an overly amorous octopus, maybe I can straighten out this mess. But I wouldn't be surprised to find that this list has picked up funky smells and bad habits from all the earlier versions of OS X I've run.
Help? Please?

Answer 1

Please read this whole message before doing anything.
This procedure is a diagnostic test. It won’t solve your problem. Don’t be disappointed when you find that nothing has changed after you complete it.
Third-party system modifications are a common cause of usability problems. By a “system modification,” I mean software that affects the operation of other software — potentially for the worse. The following procedure will help identify which such modifications you've installed. Don’t be alarmed by the complexity of these instructions — they’re easy to carry out and won’t change anything on your Mac. 
These steps are to be taken while booted in “normal” mode, not in safe mode. If you’re now running in safe mode, reboot as usual before continuing. 
Below are instructions to enter some UNIX shell commands. The commands are harmless, but they must be entered exactly as given in order to work. If you have doubts about the safety of the procedure suggested here, search this site for other discussions in which it’s been followed without any report of ill effects. 
Some of the commands will line-wrap or scroll in your browser, but each one is really just a single line, all of which must be selected. You can accomplish this easily by triple-clicking anywhere in the line. The whole line will highlight, and you can then either copy or drag it. The headings “Step 1” and so on are not part of the commands. 
Note: If you have more than one user account, Step 2 must be taken as an administrator. Ordinarily that would be the user created automatically when you booted the system for the first time. The other steps should be taken as the user who has the problem, if different. Most personal Macs have only one user, and in that case this paragraph doesn’t apply. 
Launch the Terminal application in any of the following ways: 
☞ Enter the first few letters of its name into a Spotlight search. Select it in the results (it should be at the top.) 
☞ In the Finder, select Go ▹ Utilities from the menu bar, or press the key combination shift-command-U. The application is in the folder that opens. 
☞ Open LaunchPad. Click Utilities, then Terminal in the icon grid. 
When you launch Terminal, a text window will open with a line already in it, ending either in a dollar sign (“$”) or a percent sign (“%”). If you get the percent sign, enter “sh” and press return. You should then get a new line ending in a dollar sign. 
Step 1 
Copy or drag — do not type — the line below into the Terminal window, then press return:
kextstat -kl | awk '!/com\.apple/{printf "%s %s\n", $6, $7}' 
Post the lines of output (if any) that appear below what you just entered (the text, please, not a screenshot.) You can omit the final line ending in “$”. 
Step 2 
Repeat with this line:
sudo launchctl list | sed 1d | awk '!/0x|com\.(apple|openssh|vix)|edu\.mit|org\.(amavis|apache|cups|isc|ntp|postfix|x)/{print $3}' 
This time, you'll be prompted for your login password, which won't be displayed when you type it. You may get a one-time warning not to screw up. You don't need to post the warning. 
Note: If you don’t have a login password, you’ll need to set one before taking this step. If that’s not possible, skip to the next step. 
Step 3
launchctl list | sed 1d | awk '!/0x|com\.apple|edu\.mit|org\.(x|openbsd)/{print $3}' 
Step 4
ls -1A /e*/mach* {,/}L*/{Ad,Compon,Ex,Fram,In,Keyb,La,Mail/Bu,P*P,Priv,Qu,Scripti,Servi,Spo,Sta}* L*/Fonts 2> /dev/null  
Important: If you formerly synchronized with a MobileMe account, your me.com email address may appear in the output of the above command. If so, anonymize it before posting. 
Step 5
osascript -e 'tell application "System Events" to get name of every login item' 2> /dev/null 
Remember, steps 1-5 are all drag-and-drop or copy-and-paste, whichever you prefer — no typing, except your password. Also remember to post the output. 
You can then quit Terminal.