> The fixed logic, at least judging by the commit message, still feels very shaky on correctness grounds

This was my experience as a dev on a team at Google for a few years. I saw a LOT of exceedingly lax treatment of correctness in the face of concurrency. There have even been multiple decisions I've seen to guess at how to fix concurrency bugs and just say "well, looks good to me, let's see if it does anything."

It's par for the course, and folks get (got? =P) paid handsomely for doing it.