I just tripped on this bug when launching 'xscreensaver-command -lock' from xmobar's label action. Locking via shell-script with 'sleep 0.1' before xscreensaver-command works around this problem.
- Bug#785280: xscreensaver not grabbing mouse Michał Mirosław
- Bug#785280: xscreensaver not grabbing mouse Michał Mirosław