Technical explanation... We changed the following:
1. Enabled Instant Swapping to sync the game resolutions
2. We configured a Reset Region for Swap Group 1 (Region 2) for the resolutions to be synced to.
Because Swapping was not previously configured for this Window Layout, the Swap Group did not have a Reset Region configured.
This is important because this works by initially resetting to the "Reset Region" to permanently set the resolution. This can be any Region, hopefully on the same video card... which brings us to number 3.
3. Region 1 -- on its own video card -- gets switched to Swap Group 2, and Swap Group 2's Reset Region is set to Region 1 (the existing region).
Because we are setting up Instant Swapping with a Reset Region, and because we are spanning multiple Video Cards
, we should be using multiple Reset Regions (to avoid performance penalties from resetting or moving onto the wrong video card) and therefore multiple Swap Groups. (This is basically what happens during the Window Layout Wizard if you use a Swapping enabled layout with Cross-monitor disabled.)