At first glance this seems like a bug, thanks. There have been many bugs in the past involving struct embedding, but after a quick search I don't think this is a duplicate. Want to try working on a fix with a test?
We could always merge this early in the 1.18 cycle, and see if any users complain. I would hope that noone is depending on the existing inconsistent behavior - I've been wrong on that assumption before, but not always :)