I don't have your platform to test on, but it sounds like a common focus issue. Try clicking the entry with the mouse first, before typing, or do this:

$ent->focus;
MainLoop;
[download]

Only one widget can have keyboard focus at a time, often you will see a binding like this, to ensure an entry or text widget always gets keyboard focus:

$mw->bind( '<Any-Enter>' => sub { $ent->Tk::focus } );
[download]

that will ensure that if your mouse wanders off of the app, the entry will regain focus when the mouse re-enters the mainwindow.