Fences don't work like that. Fences do not have the abilities to tie specific Fences to specific Windows Desktop. What Fences can do is to have its own Multi Fences Desktop pages. Where different Fences desktop page will have different set of Fences on it.
The issue you was seeing here:
Enabled pages and dragged a fence off to the left, not to other monitor and all get is a screen with just this fence. Go back and the other page contains nothing but this single fence. Only way back is to reload a snapshot and restart windows.
This, I believe, is a normal behavior of Fences desktop pages. You just need to familiarize yourself on how to navigate it. It is quite easy to confuse between Windows desktop page vs Fences desktop page.
Try looking here. Ref screenshot below. Click on those links (Inside the red box) to learn how to navigate Fences desktop pages.
Stardock Community Assistant