When I import XML files (from Finale), the rests in keyboard parts all have “Force Position and Duration” ON, and “Rest Pos” ON.
I can access these attributes in Write mode and in Engrave mode. In Engrave mode, I can turn off Force position, no problem. If I click on “Note pos”, the switch flicks off, then back on, but the rests move position. However, the movement doesn’t survive a close/reload.
Only if I turn off the settings in Write mode do they hold.
Try using Edit > Reset Position instead.
There are boring technical reasons why the Properties panel works differently in Engrave mode and Write mode; in Write mode, you can only set properties that can’t vary between different layouts and/or frame chains, whereas the properties you can set in Engrave mode can vary per-layout and per-frame chain within a layout. This can lead to some slightly confusing behaviour. We have more work to do to try to make it clear what’s going on in all of these situations.