The black trim is porous, and what happened was the wax got inside the pores. To remove, get yourself a simple small detail brush (toothbrush also works) spray some all purpose cleaner (simple green) on the area and scrub lightly with the brush.
The brittles will get inside the recessed area that has the wax. Rubbing it with a rag will do nothing. Once you remove the wax, apply a water based dressing and it will look like new.
Peanut butter also works, honestly. Rub some on, wash it off.
You should use a non-staining synthetic next time, like Zaino http://zainobros.com . These don't leave wax stains.
When I wax, I take masking tape and tape over the black trim below the doors etc. It allows me to wax without wasting time by trying to not get wax on the black trim. When finished just pull off masking tape.
If you pretreat all of your plastic with Mother's Back-to-Black (or equivalent), any wax residue will easily wipe off. Found this suggestion on a detailing board, tried it last weekend, and it works great.