Partially loaded level instance becomes fully loaded after editing nested level instance

Steps to Reproduce

• Create new WP level
• Place few actors and create a Level Instance with them
• Open that Level Instance and place new actors and create another Level Instance with them
• Unload all partition cells
• Load a few partition cells to partially load the first Level Instance created
• Open for edit that Level Instance
• Notice all actors getting loaded (which is expected)
• Open for edit the nested Level Instance
• Exit the Level Instance from the tool bar in the bottom middle of the viewport
• Notice that the Level Instance is still fully loaded

To fix this, you can :

• Reopen the first Level Instance
• Exit the Level Instance
• Notice that all actors that aren't part of the loaded partition cell will be unloaded