Niagara Memory Leak in vertex buffer when increasing particle spawn rate on CPU sims

Increasing the spawn rate of a CPU particle sim will cause a memory leak in the vertex buffer. 

1. Create a Niagara emitter based on the fountain preset
2. Create a system with the newly created emitter
3. Add the system to a level
4. Use stat rhi to track vertex buffer memory usage
5. Increase the emitter spawn rate to ten times the current value
6. Watch the vertex buffer memory increase.
7. Decrease the spawn rate to the original amount
8. Close the Niagara editor, and delete the system from the level

RESULT
The vertex buffer memory usage will not recover from the spike after increasing the spawn rate, even after closing the Niagara editor and deleting the system.

EXPECTED
Memory usage from the increases particle count should recover when the number of particles are reduced, and the systems are deleted/closed. GPU sims behave in the expected way.