Problems using gromit

I have installed the screen annotation tool gromit.

The tool uses the pause button on the keyboard to activate drawing, and should disable the default pause functionality. But when I click pause the screen goes to screensaver / sleep mode. How can I disable the sleep / screensaver functionality (I will never need it)?

Also, I’m meant to be able to press other buttons while gromit is active to change the colour etc. But when I click the buttons it says are set, the colour / pen style doesn’t change.

Because the actions coupled to keys are often dependent on the desktop: Please what desktop do you use?

I see, that makes sense. I’m currently using GNOME 3.14.1