Apple tends to underplay any admission of bugs in its software. It doesn't even like to use the word "bug." Rather, it refers to fixing "issues." For example, in its support article on OS X Mountain Lion v10.8.2 Update Apple notes that "an issue in which Keychain may not be accessible" has been resolved. As in this case, such admissions typically do not get posted until after Apple has released the update that fixes the bug.
However, as I initially covered back in 2008, a scrutiny of Apple's support articles can reveal information about bugs that Apple is currently working to resolve. You'll know you found one of these bug reports if the article concludes with the sentence "This document will be updated as more information becomes available." These articles provide Apple's current recommended work-around for the unresolved bug; the promised "more information" will likely be a future update that eradicates the problem altogether.
After a brief search, I found two recent examples of these type of articles.
System Preferences stops responding after viewing Desktop & Screen Saver pane
The first Apple article reveals that "System Preferences may stop responding if you select an iPhoto Event that is no longer available in iPhoto as the source for your desktop picture."
The recommended temporary solution requires force-quitting System Preferences and selecting a different valid iPhoto event. Presumably, in a forthcoming OS X update, either unavailable events will no longer show up or their selection will no longer cause System Preferences to stop responding.
Login window partially appears, cursor movement redraws screen
Another Apple article notes that "if you are logged out of your account while the display is sleeping," the login window may have an odd and unwelcome appearance (see image at top). This may make it difficult to access the text box for entering your password. To avoid this, Apple recommends setting your "Security & Privacy" and "Energy Saver" System Preferences so that it's no longer possible for an automatic logout to occur while the Mac is asleep. Alternatively, if you don't require an automatic logout, you can simply disable the option altogether--via the setting in the Advanced section of Security & Privacy.
Again, a future update should permanently fix the problem--so that the display oddity no longer occurs under any circumstances.