When the background image, saturation or brightness are changed rapidly, the successive requests are all processed immediately, rather than being discarded. Since changing the desktop background is an expensive operation, this results in the entire desktop stalling for several seconds, while using 100% of the CPU. This bug can be triggered from the xfdesktop-settings dialog, in a few different ways: -Selecting a desktop background from the list, and holding the up or down key. -Focusing on the brightness or saturation slider, and holding any of the arrow keys. -Scrolling the mouse wheel while focused on the brightness or saturation sliders. I suspect this bug is also the reason that brightness and saturation are controlled purely by sliders, rather than having an associated spinbutton, which makes for a fairly awkward interface.
This has been fixed in xfdesktop4.11, the saturation and brightness sliders are gone and changing wallpapers rapidly doesn't eat all CPU anymore nor does it happen sluggishly.