Yeah, I've tried prying it loose with a thin piece of plastic, but it just won't move. I'm waiting to see if the shop I got it from can contact Yamato, and see what they recommend.
You can talk to GU-11 and Macross_Fanboy, as they've had the same problems with their recently purchased VF-1Ds. I've had experience with Yamato Valks before, and believe me, this is not a normal issue.