Sidebar folders don't "spring open" any more

Question

I've seen this behavior on a number of Macs (including mine). At some point the ability to drag a file onto a Finder window sidebar folder and have that folder "spring open" to show its contents has disappeared. All other drag & drop works fine and the spring-loaded folders ability on all other folders (in Finder windows or on the Desktop) remains.
It's just the Sidebar folders that refuse to spring open. Note I can still drop items on those sidebar folders and have the dropped item moved (or copied).
My Intel iMac (OSX 10.4.6) now has this problem whereas my new Macbook works fine. I'm pretty sure there's some app I've installed that's pooched this. Im also pretty sure I saw this problem (and the answer to it) posted somewhere. Any help will be appreciated.
Thanks,
Barry

Answer 1

Barry,
Plist files contain instructions for recording and executing tasks associated with the the application or function that owns them. They can and do become corrupted. If you look in the ~Library/Preferences Folder you can usually guess what application or function the .plist serves by analyzing the file name. In your case com.apple.sidebarlists.plist was the suspect.
Proper identification of the appropriate .plist is not always so obvious, but for example com.apple.iCal.plist is the preference file for iCal. When an application malfunctions, removing the associated .plist file from the preferences folder to the Desktop is often the best first troubleshooting step.
If you have a problem with an application, Quit the application, find the associated plist file in the Preferences Folder, and move it to the Desktop as a first step in your troubleshooting procedure. Then log out/in or restart and re-evaluate the performance of the application.
A new default .plist file is automatically created in your Preferences Folder after you remove the recalcitrant .plist and initiate the log out/in restart sequence. You can expect default application behavior and you will have to reset some preferences. If the application or function returns to normal after removing the .plist file, it will prove that the original file was corrupt, and you can now safely trash the .plist file which you placed on the Desktop.
If the application or function is unsatisfactory, the original copy of the plist file which was placed on the Desktop can be safely returned to the preferences folder. Just allow the system to replace the newer plist.
If you are having problems with any aspect of OS X, experiment with deleting the appropriate .plist file. Plist corruption is common and .plist file deletion often cures many problems. Too many users try intricate solutions first and end up complicating their problem.
;~)