in reply to
ref to read-only alias ... why?
Whether you get an alias or a copy of a read-only value is a bit of an optimization concern and it has changed previously. I'm not terribly surprised that it has changed again (and seems to change based on features of Perl you include and may have changed several times in just recent versions). I would consider Perl code that depends on this behavior to be broken much more so than I consider either behavior to be a bug in Perl.
You really want it to be a Perl bug unless for(1..3) makes $_ read-write while for(1,2,3) makes $_ read-only?