When the mouse pointer is on the canvas, and a tablet is active, the canvas stops responding to mouse actions as long as the pointer remains inside it, even after the tablet is put down. For example, the arrows on the rulers do not follow the pointer, and the mouse buttons don't work. Additionally, holding space to pan does not work - the pointer changes, but mouse movement is ignored.

Workaround: Move the pointer outside the canvas, then move it back onto the canvas using the mouse, not the tablet. Mouse functionality will then be restored.

The bug is only triggered with the canvas area inside the image window. Anything else (e.g. dialogs) do not cause these effects.

If I recall correctly, GIMP 2.6 did not exhibit this behavior.