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 (2.14) 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 values overriding the environment (GREP_OPTIONS)
is more significantly more useful.  Though even make files
add to their own ENV vars and append to them -- so it seems
later options overriding earlier options would be good in that
case too.

But without cmd line overriding GREP_OPTIONS, then there seems
to be no way to specify various defaults.