Thought the pva might off showed the bubbling if you got more to do give it a good scrape first if it's still their when you go back scrape it back and either easi fill or do the area again nothing worse Micky
On backgrounds that could cause problems i have a hand wood saw. I have removed handle and cut blade in half. Drag across surface to break back to background. It scratches lines back to good surface. Seal then skim.