Looking at your code on github, it's because of this: 
my $canvas = $Mainwin->Scrolled('Canvas')->grid;
my $real = $canvas->Subwidget("canvas");

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Based on your choice of the variable name $real, you seem to already know what the issue is here :) $canvas isn't a 'Canvas'.

In reply to Re^7: Question about embedded Tk::Canvas by kschwab
in thread Question about embedded Tk::Canvas by emilbarton

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