Thanks for testing!

...must have been fixed in the meantime! (?)¹

> perl -v

This is perl, v5.10.0 built for i486-linux-gnu-thread-multi
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to which class does $x belong to? still IO::Handle ?

... ARGHHHH ...

Did you explicitly use IO::Handle ?

My examples work now after importing.

> perl
use IO::Handle;
my $x=\*STDOUT;
$x->print("hu hu");                 
__END__
hu hu
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update

¹) 5.12.0/perldelta.html#Other-potentially-incompatible-changes

Filehandles are now always blessed into IO::File .

The previous behaviour was to bless Filehandles into FileHandle (an empty proxy class) if it was loaded into memory and otherwise to bless them into IO::Handle .