This didn't used to happen to me before but when I switch back to my default workspace, it makes the thumbnails super tiny and changes the size of my bridge window and some other characteristics. I've tried to save it the way I want it under different names and it never works.
Peter Katoff commented
Are you using the grid layout for thumbnails? The behavior you describe will happen if you switch workspaces with grid layout selected. This really should be fixed. But in the meantime:
Solution 1 - switch to a different thumbnail layout. Problem will go away. Only affect grid layout.
Solution 2 - If you really like the grid, then when you switch workspaces select a different thumbnail layout and then immediately select grid again. An inconvenient workaround but it will fix the thumbnail layout issue.