in reply to what patchlevel perl-5.8.0-rc2 corresponds to?

RC 2 is change 17431 - the only difference to the snapshot you have is the missing patchlevel output in perl -V.
You will notice perl -v doesn't say ...with 1 registered patch.

It generally is a good idea to try out developer snapshots of perl and feed your feedback back (;-)) to - preferably using perlbug.