I hate resin vehicles.
No matter how many times I wash them, I can never get all the mold release off. So, when I spray them their base color, the paint does not adhere properly. Sometimes, not at all. Sometimes, you get this leprous effect.
I just tried, again. I am using hot water and dish detergent with a toothbrush to scrub into the corners ans such. Washed twice. Rinsed under running hot water. Dried thoroughly. Spray with Army Painter desert armor color (Flames of War British vehicles). Paint starts to do that 'pooling away' thing.
So I tried shooting with my preferred undercoat for metals, black Krylon primer. And lo and behold, no problems. I think I have solved an old problem for me - hit it with the plastic approved Krylon primer and then go back with the real undercoat color. Once the black dries, I will go try it.
Just thought I would share this tip.