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.