Dual monitor set up on Win7:
When using the secondary monitor for the main SU display, and placing dialog windows for Entity Info, Layers, Styles, etc (secondary windows) in the primary monitor…
Then changing the primary display to the other monitor with SU open, the secondary windows move off the viewports of both monitors, out into space somewhere. This includes the SU start-up page.
The only way to recover the secondary windows again is to go back to the previous primary monitor (from the Control Panel), where the secondary windows re-appear on the non-primary screen. They can then be placed back on the primary display, and saved by closing SU.
Sound confusing? You bet!