Same here when I had my original. And I turned and took the head off multiple times with no issue. This was the first I'd heard of it.

 

What is the purpose of the silver paint across the helmet?

 

To mimic weathering I guess?

Tho it comes off more as a Premium QC error.

 

I think it was intended to be a wash going over the whole back of the head too, mine's similar but also clumps up before the halfway point like yours. The solicited pics have a wash over the whole head, you can see the silver on his 'mohawk' and flecks on the antenna. My in-hand Premium is more like yours, with a silver 'headband' but further back is clean

 

Mine came with a deformed head so I swapped it out with the first release and painted my own highlights. Probably should buy another to see if I'd like the effect on display