Screen transition causes weird 1-frame... thing

I'm working on a game, and for some reason, when loading a screen, I'll get thos weird 1-frame... thing happen. I think I know WHY it is happening(probably scrolls isnt updating enough) but I dont know how to fix it. Just move off the screen to the right and you'll see what I mean. It doesn't happen in Slimeguy, so I'm not sure why it's happening here I'll be sure to include whoever's helps(or at least tries) in the ending credits. Thanks! EDIT: with lotsa tinkering, I fixed it. Yes, it is going to be an ESA clone.