Occasional error message popups when closing a source code tab

[anton-tchekov]

Sometimes when I close a code tab using Ctrl+W, I get a popup with an error message like the following:

Error: bad window path name ".pb.nb.f12"

bad window path name ".pb.nb.f12"
bad window path name ".pb.nb.f12"
    while executing
"winfo pointerx $w"
    (procedure "tabHelp" line 4)
    invoked from within
"tabHelp .p.nb.f12 473 639"
    ("after" script)

Here are some screenshots:

It does not cause any other issue, just the popup.