xscreensaver strange behaviour

[Giorgos]

I've made the following script to load zsnes while disabling screensaver
and power management:

#!/bin/bash

xset -dpms
xscreensaver-command -exit

zsnes

xset +dpms
xscreensaver &

exit


When I launch this everything goes correctly, xscreensaver is killed and
power management stays off while zsnes is running. If I launch this
script from the terminal though, xscreensaver is not started afterwards.
It's only started if I launch system monitor from the menu, at which
point it writes on the prompt:

xscreensaver: 12:17:52: 0: unrecognised ClientMessage
"_GTK_LOAD_ICONTHEMES" received
xscreensaver: 12:17:52: 0: for window 0xa00001 (xscreensaver)

And it's killed again.

Any help?