Panning Problem/ not panning but showing "find" dialog

I have a trouble with panning as I work on a somewhat big project.

When I want to pan the canvas I push the mouse-right-button and start dragging, but it does not pan but only shows small "find"  dialog.

This happens irregularly but very often, and very annoying problem.

I want this problem to be fixed urgently...

In the meanwhile, is there any workaround?