Why does a wash remove paint to bare plastic?

[Norm]

What I see is that a small area of paintwork goes back to what looks like the grey plastic, but that the immediate inter-face, where the removed colour meets the remaining colour can have a very thin white edge, like desaturated colour. I have had this on vehicles as well.

It is never in the middle of a flat face, but typically happens around the area of what may best be described as an undercut.

Interestingly and what caused this post was that on recently painting 3 German officer figures for a Zvezda HQ stand, 2 out of 3 had this erosion around the gun holsters, 2 had it around map cases held on the belt and all 3 had it at where the trousers meet the long coat. In fact on looking at a recent photograph that I put up on my blog last week, it looks like I have totally missed repairing one of the latter.

In the below photo taken from the recent internet posting, the officer on the right has this desaturation at the top of his right boot and I recall the motor cycle also having some similar issues, but can't remember exactly where.

[Peithetairos]

If the miniatures are soft plastic it is quite possible that paint flaking is an issue. From the picture it does look like an accumulation of wash and not the surface showing.

[Norm]

Thanks, yes I think an accumulation of wash is probably right. I have just seen in happen in another model and it is exactly in places susceptible to accumulation. I think because I rather thin the wash, I feel free to just lash it on and need to take the time to lift out the pooling. This time I reduced the variables by only having water in the wash and allowing the primer and paint to properly cure, so I am fairly convinced it is pooling that is the problem.