Memory usage spike during PIE doesn't reduce after play session

When opening the editor the memory usage jumps during PIE. After exiting PIE the memory use does not go back down.

1. Open the Windows Task Manager and go to the Processes tab
2. Open a new Third Person Template project (UE4Editor.exe mem usage ~630,000K)
3. PIE (mem usage jumps to ~700,000K)
4. Exit PIE

Result:
In one test the mem usage dropped to ~685,000K and in another test the mem usage went up after exiting PIE to ~715,000K

Expected:
Memory usage returns to pre-PIE level after exiting.