As it turned out, my "raw guess" was a direct hit -- so to make it easier to find for future "searchers", I make it an answer as promised:
This problem is mostly caused by the fact that something got messed up with the apps' cache and/or data. So what you should try first is:
- Go to Settings → Apps → Manage Apps
- Select your launcher
- Hit the button labeled "Clear Cache"
If that doesn't solve the issue, take the same steps -- but in the last step hit the "Clear Data" button (note: This will reset the launcher configuration as if you just removed the app and did a fresh re-install).
If you still had no luck, you could simply uninstall and re-install the launcher (as long as it's not a system app). This will do all the above, but additionally remove (and on re-install re-create) the apps Dalvik cache. Count it as "partial factory reset".
Having mentioned the dangerous word: A factory-reset can serve as a "last resort" (as it cleans the entire device) -- but you would lose all your data that way, and needed to re-configure everything anew. In case you have to do that (I don't think it is necessary for your case here), take care to have a backup of as much of your data as possible.