I haven't ever seen this happen, but if quitting apps and hard resets don't do it you might want to start clean. Are you able to run a backup of your iPad mini? If I was in your shoes, I would back up the iPad, erase the iPad and then restore the data to see if that fixes it.
- Step 1 would be to back up the data (see http://support.apple.com/kb/ht1766).
- Step 2 would be to restore the iPad to factory settings (see http://support.apple.com/kb/HT1414).
- Step 3 would be to restore the backup (see http://support.apple.com/kb/ht1766).
Hope this helps!!