Forge World does leave a bit more mold release on their bits than most.
Crazy as it sounds I use toothpaste on pretty much all my minis before I paint them (after I am done cleaning all the mold lines and filling gaps ect.) It Leaves a nice smooth surface, removes the mold release and cleans up any residue and mess left from the cleaning up process.
I read somewhere on the internet, probably here on dakka that toothpaste has tiny polishing beads or whatever... Can't fully remember.
Bottom line...use a spare soft bristled toothbrush with a tiny dab of toothpaste and some warmish water (just a bit warmer than room temperature) cleans up any mold release residue and leaves a clean surface for the paint to stick to.
This also works wonders for old metal minis that tend to form a layer of gunk over them over time. After doing this it leaves the metal shiny new and all that gunk that would hinder the paint from sticking is gone.
You really notice a difference when painting after it is primed well on top of this, the paint just seems to stick more,
IMO anyway...
It also leaves your minis smelling minty fresh!