Thanks to you all!

Those fisheyes (good to know a name for the EVIL) are indeed special. I painted dozens of parts that way and found this particular effect only on these two parts, on these two doors from the dashboard.

The special thing is that it happens again after grinding the paint off to the bare metal, cleaning again and priming again - at the same place (and of course at the second time you'll do it carefully).

So I wonder if there is some grease or anything in that old piece of metal itself. If there may be some microscopic crack or pipe or blowhole in the material that allows any residue to stay there.

I'm going to try again, sand the color down to the metal again, may be I'm going to warm it up and let it rest in solvent for a day and clean again using acetone and let it dry in a warm area for a while. I'll coat it with primer and put it in the oven for an hour and sand it slightly and may be do a second pass with primer - and then try again with light coats of paint.

The idea was to quickly re-coat these two parts in black before reinstalling - now I spend some hours for them...