100% it's your paint. Stickers don't like matte finish (should have been gloss or satin). You have to watch what type of gloss you use also. Best to use an oil based enamel, so avoid water based if you can. Also, avoid bathroom oriented paints that have teflon and other chemicals added for cleaning and mold reduction. These additives can adversly effect the paints surface energy. Depending on the quality of the art, you might get away with peeling it off very carefully, painting, and then reappling with one of those 3M spray adhesives.