When I paint on an image, if I press the space key, it allows me to move the view. Then, after I have clicked on a panel, for instance to change the opacity of the brush, the space key has no more effect.
I need to click on the canvas to recover that function with the space key. It can be annoying because this click make a paint trace on the canvas. A right click restore the function too. I think it's a matter of focus.
Please note that the effect of focus loss is the same on zooming with mouse wheel.