A lot of guesses, by me and ++bliako: no resolution.
I was tempted to raise as doco/bug issue:
the current target being "Active bugs for Tk",
but that is shutting down in a couple of days.
I'll wait and see what happens.
I'm still using this function.
I did determine a number of things.
Two things of note:
-
An update of the UI ($mw->update) is entirely unecesssary;
an update is necessary, but only of the canvas ($canvas->update()).
-
Depending on your use case, you may be able to exploit the ability to
compose individual items, as well as groups, into a single group.
I found this to be useful, YMMV.