No longer able to rotate on axis with rotate manipulator

I’m not sure what I’ve done, but I can no longer rotate an object by selecting one of the axis when the rotation manipulator is on. I’m in object mode, and I can rotate in screen space using the white circle that surrounds the manipulator, but not by dragging on any of the other axis circles. The translate and scale manipulators work fine.

Instead, it appears to act like the axis don’t exist, and “clicks through” and starts dragging the object around.

is there some preference thing that I’ve missed?

OK - found the problem. Apparently an OpenGL issue - so I had to selection to use “OpenGL Occlusion Queries”.