Question: I have several apps from the Mac App Store and I noticed that installing updates doesn’t work normally. The store doesn’t consider the app updated. I repeated the updates and it didn’t solve the problem.
Answer: This is the kind of odd behavior that often is fixed by deleting associated files. In this case, two .plist files are concerned.
Please note that in order to get this done, you first need to access your Library. If you are running OS X 10.7 Lion, you need to make it appear first.
With your library available, follow this path:
Startup Disk > username > Library > Preferences
Then, you need to find two files:
com.apple.storeagent.plist
com.apple.storeagent.plist.lockfile
Move them to the Trash and restart. Your apps should update for good.