Hello Josef,
Thank you very much for the bug report. I'm sorry it took over 8 years for me to look into.
I just tried to put an AbstractCanvas object into a grid and it seemed to work as expected.
I also made a new Frame object inside the AbstractCanvas and used grid to arrange a bunch of buttons there and that all seemed to work correctly for me too.
Please let me know if you still might have an example which does not behave as you think it should.
Thanks again!
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-Pip@CPAN.Org