Oops, not what I was thinking at all!

Here are shorter example demonstrating the bug in more detail:

perl -e 'sub new{print@_} main->new(); open main, "foo";'
perl -e 'sub new{print@_} main->main::new(); open main,"foo";'
[download]

And the message from the second one gives a pretty solid indication what is going wrong. (I think that this is perlbug material.)

UPDATE
Since tye complained, the outputs respectively are:

Can't locate object method "new" via package "IO::Handle" at -e line 1
+.
GLOB(0x80d4208)
[download]