Pressing the right Shift, Control, or Alt key on Windows (checked only with Tk 8.5.7) produces
correctly an event with a ..._R keysym. However releasing the
same key produces an event with a ..._L keysym. The same works as
expected on X11 systems.
The bug was originally reported for Perl/Tk. See
https://rt.cpan.org/Ticket/Display.html?id=47173
For your convenience, a test script is attached.
Regards,
Slaven
keysym test script