Corners of open windows look weird

Question

hi guys
this started from one or two updates back, and has been going on ever since, does anybody else experience this? any help is appreciated?
http://i41.tinypic.com/2v9dm3t.png
if you look at the screenshot, where all windows' rounded corners are, there are dark normal corners visible as if the transparency masks are not applied properly. this happens on the built-in display. i have no other display attached.
points of note:
# i haven't installed any apps that may interfere with the display.
# i believe my display adapter is fine. i use the computer constantly.
# i have applied all updates.
# have no other problems whatsoever. nothing is garbled, dock and everything else runs fine.
# bottom corners of windows and their shadows look fine (but those corners are not rounded anyway)
# the effect seems to be random, and some windows sometimes have it, some don't.
# this is not a one-off occurrence, log-out/restart does not fix the problem.
things i've tried
# changing display colours and resolution.
# changing colour profile.
# switching between blue and graphite in preferences
# repairing permissions and/or safe-booting by holding shift.
things i don't want to try:
# reset pram and related
# take my mac to a genius
thanks.

Answer 1

http://discussions.apple.com/thread.jspa?messageID=3539383&#3539383
http://discussions.apple.com/thread.jspa?messageID=3681668&#3681668
I glean from the above articles that this may indicate problems repairable with Disk Utility.
Boot from the installer disk, select language if applicable, choose utilities, run Disk Utility and verify (and repair if necessary) the drive. Then boot from your main drive in Safe Mode and repair permissions (doing it while booted from the main drive uses an updated version of permissions).
[Resolve startup issues and perform disk maintenance with Disk Utility and fsck|http://docs.info.apple.com/article.html?artnum=106214]
[Using Disk Utility in Mac OS X 10.4.3 or later|http://docs.info.apple.com/article.html?artnum=302672]
[Disk Utility's Repair Disk Permissions|http://docs.info.apple.com/article.html?artnum=25751]
From BDaqua (couldn't have said it better):
"Try Disk Utility
1. Insert the Mac OS X Install disc that came with your computer (Edit: Do not use this disc if it is not the same general version as what you have currently on your computer, e.g. use a Tiger disc for a Tiger drive, not a Panther disc), then restart the computer while holding the C key.
2. When your computer finishes starting up from the disc, choose Disk Utility from the Installer menu. (In Mac OS X 10.4 or later, you must select your language first.)
Important: Do not click Continue in the first screen of the Installer. If you do, you must restart from the disc again to access Disk Utility.
3. Click the First Aid tab.
4. Click the disclosure triangle to the left of the hard drive icon to display the names of your hard disk volumes and partitions.
5. Select your Mac OS X volume.
6. Click Repair. Disk Utility checks and repairs the disk.
Then Safe Boot, (holding Shift key down at bootup), run Disk Utility in Applications>Utilities, then highlight your drive, click on Repair Permissions, reboot when it completes."