Vinyl contains a large amount of plasticizers. Plasticizers are chemicals added to plastic and rubber compounds to soften and improve the flexibility. Plasticizers can come out of the vinyl and migrate to the surface of the vinyl, softening solvent-based inks. Fugitive glue is a plastic compound with a very large amount of plasticizers; the staining of the substrate is caused by the migration of the plasticizers. Try printing the inserts with UV inks.