I'm not sure if these behaviors are intended. I use the browser as a model. These might apply also to other programs.
1. When the browser is within the isolated account, and it is restarted (i.e. by add-on request, etc.), the browser closes and will not come back, unless it is started by the user again.
2. If the browser is already open in the isolated account, then I switched to the main account, and then open the browser again using its shortcut in the main account, it would say "Pale Moon is already running..." and then closes.
For the second item, I suggest that the program within the isolated account should be called. And so, if clicking the shortcut in the main account happens, the browser that is already open within the isolated account should be opened again. It should be like restoring a minimized program.