I find rebooting the iPad is not necessary. quit Mpad, double-click the home button, hold Mpad until it wiggles, click the minus-sign. Home button. load Mpad. refresh album art.
In fact I do this al the time after loading new songs, because Mpad in my situation also shows wrong album art form other albums....

updating the database is the preferred method when the above has not helped enough, but the above is always the first step.
hope this helps,
Marius
Sometimes various Aps will do funny things on the iPad. Try rebooting the iPad -- that will often get rid of the Ap gremlins.
Tony