huh, that's one of the cases the dialogue *shouldn't* show up, haha!
Well, okay, i have a decent guess what's happening. My best bet is your particular desktop constructor is improperly flagging the form as visible even if it isn't because the process manipulates its contents while hidden; just before. I will try to force-hide it just before showing it as modal and see if that helps.
Is there somewhere i can send you a test build? mail or discord?