The inverse of this is when there's a glaring error in a design (we all write bugs - this is just a design bug) and the front end dev implements that in the final product. Of course, other processes (QA, Design QA, etc) has to fail for this to go through to production...

I don't think we need FE Devs who are full on designers, but FE devs who are design 'aware' are, in my experience, much better.

Yes, I think they should be able to tell when a design is off, but that's different from design skills.

Developers need as much a design ability as designers need engineering ability.

If only every company actually hired real designers...