I know this is an old post but do you have a specific link for the foam backup tape you referenced? Also, do you completely prime everything and have it 100% ready to go prior to painting the jambs? Or do you paint the jambs, assemble and then still have some wet sanding, etc to do?
https://www.amazon.com/3M-06298-Soft-Edge-Masking/dp/B0012RUGMC this stuff? there are a few diffrent sizes
He simply either used no ground coat, or the incorrect colour groundcoat, Id put money on that. A sun gun helps with seeing coverage.. Id also hazard a bet that the doors were done towards the end of the paint tin where more metallic particles settled between stirs and pours while doing everything else first.. when soft edge masking, people gotta be careful too much groundcoat doesnt get in your soft masked edge.. i do the soft edge masking on a hideable line in the shut, then another one over top further out i can pull off through the door gap once ground coated.
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