There is a bug with flwm_topside. Hard to believe that Private Preview QA and Public RC did not catch it.
I personally do not use flwm_topside, thus gives me pause that perhaps I should switch to what I do use, flwm the classic version.
The fix for topside is:
/usr/bin/flwm_topside_restart
#!/bin/sh
kill -s USR2 `pidof flwm_topside`
.wmx/Refresh_Menu
#!/bin/sh
exec flwm_topside_restart
It is only the /usr/bin/flwm_topside_restart that is crucial, so adding
usr/bin/flwm_topside_restart to /opt/.filetool.lst
(note no leading / ), should make dynamic menus work.