Mouse Cursor Jumps Back To Starting Point
While the GUI was active, moving the mouse would only work for a few seconds or fractions of a second, after which the mouse cursor would jump back to its starting point. Wherever the mouse cursor was when I started up the system, that was the position it would return to automatically after too brief a time to make proper use of the mouse. (The cursor would reposition even while I was trying to move it to another location, such as to launch an app from its icon.)
First step in resolving this was realizing a potential hardware conflict between input devices. I had both a Wacom Intuos3 tablet and a Logitech Marble Mouse (trackball) active at the same time. The tablet was configured to have "absolute" as its main pointer mode, rather than "relative." With the tablet mouse on the tablet, but my hand on the trackball, the tablet was overriding what I was trying to do.
This provided a fairly easy fix: Use Sax2 to set the primary mode of the tablet to be "relative" so that the mouse on the tablet could "virtually" follow the motion of the trackball. The pen can still be in "absolute" mode. I do see some quirkiness in moving the mouse cursor with the tablet mouse, but that device seems quirky anyway, which is why I generally use the trackball except for things where a pen is a better interface (e.g., image editing).