This can be easily reproduced in Wish (8.6.11):

% pack [canvas .c]
% .c create rectangle 10 10 90 90
1
% .c bbox 1
9 9 91 91
% .c create rectangle 20 20 80 80 -state hidden
2
% .c bbox 2
%

I doubt this is a bug because the docs (https://www.tcl.tk/man/tcl8.6/TkCmd/canvas.htm#M36) say:

> if the matching items have empty bounding boxes (i.e. they have nothing to display) then an empty string is returned