Edit: Didn't find any leaks. Anyway, just killing units also increases memory usage, and so does using an effect for the first time.
You should see if it still increases memory usage after the first cast (and without killing any units).
I thought Shockwave created a terrain transformation leak (which cannot be fixed), but my memory didn't increase by that (so I was wrong, I guess?)
The spell is not MUI, so I assume that wasn't your plan?