I see in your skin, the “FORM” skin section has two states defined and colors of form are different for these states.
Try to change color of FORM, make this color equal for both states. Maybe it's a reason.
Write here if this solution don't work, I will need a demo in this case.
Still does the same thing. It's not a big deal, just something I noticed. If you still want a demo let me know what is needed. I can zip up the project if that will help.