I encountered a bug in the Lightroom 5.2 spot removal tool. When the tool is active (after hitting Q), perform a left-click with the mouse and hold it. Then move a little so it starts painting a white surface. Still keep the mouse button pressed and hit the Delete key to remove the spot being created. Instead of deleting only this spot, ALL spots disappear.
After this toggling spot removal mode does not work anymore.
Restart of Lightroom is required. I use Windows 8 Pro.