bug#15127: grep not taking last conflicting option as choice?

[Linda Walsh]

Isn't it usually the case with conflicting options that the last
one gets taken as the choice, with choices on the command line
overriding choices in the environment?

Grep doesn't seem to follow this convention.

Is there a reason why grep doesn't or did it
used to and now chooses to do nothing in the case of
conflicting options?  (eg. -P v. -E)

I think the earlier behavior, especially in respect
to cmdline value overriding the environment is more
useful otherwise lines built up both by successive passes
in make files and with those who specify defaults in GREP_OPTIONS,
but expect cmd-line usage to override ENV...

(coreutils 8.21)

(or is grep not part of coreutils these days...hmmm...)