Onig discrepancy solved?

FWIW, this line in Oniguruma's regenc.h (5.9.2) is commented.

If you un-comment it, you get an ONIG.DLL which behaves like the one distributed with v11. In particular, it fixes the errors I pointed out in FFIND, @REGEX[], and my GREPP.

Rebuilding ONIG.DLL would seem an appropriate thing to do.