[ubuntu] mouse pointer disappears - how to reset

ubuntu 15.10
thinkpad x250 with docking station and two exteal monitors - mouse in docking station

'Sometimes'[0] the pointer for my mouse disappears. The mouse still controls the position of the mouse because I can see the focus change as I move it around - that's the only way I can see where the mouse actually is.

Is there a way to reset this without restarting the window manager or logging out?

Is there a bug filed for this? The ones I find in launchpad seem to be related to specific actions and not one I actually do...

Regards,

Max.
[0] I've not been able to identify any specific circumstances when it happens :/