Randomly disappearing DVD artwork in iTunes

Hello,

Hopefully someone can help me...

I was lucky to receive an Apple TV for Christmas which is working really great. I have been ripping my DVD's on a daily basis using Handbrake to great effect, playing very well through my Apple TV.

However, my problem lies in mysteriously disappearing DVD cover artwork. Once I add a DVD rip to my iTunes library I select the movie in itunes, bring up the info window and goto the Artwork tab and paste in the artwork. This simply doesn't work? I have tried both pasting in the artwork (jpg saved from web) and also saving the jpg to a folder on my mac and trying to insert it using the 'Add' button. The artwork for both methods appears in the window but as soon as I click OK, no artwork appears.

Now the strange thing is, if I click to play the movie and let it run for a few seconds then close it, I can add the artwork OK. Very strange!

However (again) once I see the artwork in iTunes if I click the movie (one click) the artwork disappears!

There seems to be no pattern to this that I can detect? Some movies keep the artwork, some don't.

These are all DVD rips from disks in my iMac ripped using Handbrake and all cover artwork is from either Amazon or the iMDB website.

I should add as a further piece of information that this problem is not apparent for my CD rips and album art. Mostly iTunes finds artwork for my CD's but on occasion where it doesn't the copy and paste from the web works just fine.

This problem is only with DVD artwork.

Any help advice appreciated.

Thanks