I also have this problem. Whenever I walk, jump, or even crouch on planted crops, they break to normal dirt blocks dropping just the crop.
This doesn't seem to affect empty crops or crops with naturally grown seeds/weeds.
This DOES happen in SSP, and it HASN'T happened for me in IC2 v. 1.95b.
Is there anyway I can fix this? I wouldn't mind delving into some code or a quick fix.