Finally, found a solution for this:

From #696855 - How do you hide the mouse pointer under Linux/X11? - Stack Overflow; I heard about unclutter, so just ran

sudo apt-get install unclutter

And then put the following in a script on the desktop, called, say unclutter.sh:

unclutter -idle 1 -root -grab -visible

... and make sure you've done chmod +x unclutter.sh.

Then, after the mouse pointer disappears after suspend, use mouseover of icons to target the script and run it; this will start unclutter, which will simply hide (the already invisible) mouse pointer after 1 second of mouse inactivity; but then when you move the mouse after that, finally the mouse pointer will show :) ... however note that to stop unclutter after that, you'd have to do from terminal:

sudo killall unclutter

... as unclutter would be, at that point, running in the background.

Note: also tried, via #15 / Bug #337926 “vino: mouse cursor stays in upper left corner” : Bugs : “vino” package : Ubuntu, to use:

xdotool mousemove 100 100

but this does not make the mouse pointer show again.

Btw, one can look in the synergy source, WebSVN - synergy - /trunk/, and the "reset" of the mouse pointer seems to be coded in ./lib/platform/CXWindowsScreen.cpp.