My side panels, that I organize in two groups of three tabs, one on top of the other, get re-organized from time to time.
They get reset to the default arrangement of four tabs whenever I quit Rhino while it had a huge file open (using 8 GB of RAM). The problem shows even if I patiently wait until the process has cleanly finished before opening another instance.
Only the side panels get reset; all my custom toolbars stay where they’re supposed to.
V5 SR9 x64