An Interpretation of the POSIX regex Standard [pdf]
dn790006.ca.archive.org
1 thread
Needs [2003] in the title.
It has a list of regex'es which behave differently in different regex implementations, but does not name those implementations. Pretty disappointing.
Also very out-of-date, but https://wiki.haskell.org/Regex_Posix#Results_and_Bugs "names and shames."