I just found out a little bit about the leak.

Using the original Date::Manip code, there's a line in the _parse_datetime_iso8601 function which looks like:

   ($y,$md,$d,...) = @+{qw(y m d ...)};
[download]

where I just matched on the regexp from _iso8601_rx. If I comment this line out (and just set $y,$m,$d to some static values), there's no leaking. Note that I STILL match the regexp, I simply never refer to the %+ hash.

Unfortunately, I wasn't able to reproduce this in a simple test script, so I still need to investigate further, but I think this is an interesting result.