Oddly, I've never had a problem with it.

I only use WAB at the very top level of a program, not within another dynamic construct.

I think it would be easier to assign to a variable in the while loop, rather than changing some other for loop or other constructs to avoid bound-up $_ variables. while(my $line= <$fh>) ...

Tell me, why is it "by design" that WAB doesn't localize $_ implicitly? I know it's by design that this shortcut syntax uses $_, and lots of things do.