Here is another new thing then. To quote Dan Sugalski about $1 etc in response to my claiming once that they were local:

No they aren't. They're mutant pseudo-scalars attached to the underlying optree, and you may well get a $1 from the last time you matched that regex. (I've got a trivial program that shows the problem with a recursive call)

(His "trivial program" causes threaded Perl to core-dump.)