Album covers and video previews mixed iPhone 4

Since Ive updated to 4.2.1 the album arts started to mix with video preview pictures. For example, I have the Resident Evil 4 movie and its cover mixed with the one of Recovery album. I mean the recovery album doesnt have its art, it has like a screenshot of the beginning of the movie... This problem can be solved by deleting and then synching again the whole music library, BUT whenever I have even a video, the art mixes again and again, the art sometimes changes when I reboot the device...
The second thing is that when I sync a new album, the coveк doesnt appear in the lockscreen, I mean the music is playing and I actually HAVE the cover, it shows in iPod, but doesnt appear on lockscreen.
Are all these bugs of 4.2.1 or I have to do something to solve them? I DONT have jailbreak, people say that they some times encounter problems like these if they have it...
MacBook Pro Mac OS X (10.6.6)