Subject: | UNIVERSALL::isa is not reentrant |
UNIVERSAL::isa uses a global recursive flag.
If a custom ->isa method itself calls UNIVERSAL::isa anywhere
recursively within the ->isa method, this flag is falsely true.
This results in the intended effect (magically chaning a UNIVERSAL::can
into a ->can, which I think is wrong anyway, but lets not deal with THAT
in this bug) not happening.