Are you talking about Tk::Entry? See http://search.cpan.org/dist/Tk/pod/Entry.pod#DEFAULT_BINDINGS

The F18 key (labelled Paste on many Sun workstations) or Control-y inserts the contents of the clipboard at the position of the insertion cursor.

On my win32 machine, ctrl-y doesn't work, but ctrl-v does and behaves the same.

If you want to change the behaviour, you will have to override the binding, eg

$ent3->bind('<<Paste>>', sub {  .... } );
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