i agree, especially since grep has the same 'unimplied' aliasing of $_.

Right, that's what I meant about discarding changes being reasonable, but possibly in an "unperl-like way"

Remember that with grep changes made to $_ propagate in both directions, effecting the source as well as the returned values: "Note that $_ is an alias to the list value, so it can be used to modify the elements of the LIST."

That side-effect of changing the source values was probably a bad idea and getting rid of it in "extract" would be all to the good.

It is a good point that it's hard to see why you would want to discard a modified $_ in the returned values -- if so, then why did you modify it?