There are some resins that tend to sweat if not mixed in the proper ratio or are not mixed well enough. Cleaning with acetone or isopropyl only fixes it for a short time. The paint will stick at first, and then as the piece sweats again, the paint will rub off. There is a way to seal it, as I've heard a guy in the UK use some local stuff (that I can't remember now) that managed to stick and seal, and would take paint well. I guess you have to experiment.
Eventually it will stop, but I've had a piece that I've cleaned with isopropyl several times over a two year period, and it still has issues.
TazMan2000