Don't know if this is a factor, but I see this in the Win8 Host's Scheduled Tasks:
Name: Optimize Start Menu Cache Files-S-1-5-21-4075228474-1082787419-3685243060-1001
Author: Microsoft Corporation
Description: This idle task reorganizes the cache files used to display the start menu. It is enabled only when the cache files are not optimally organized.
On second look, I'm doubting that this is a factor. It relates to the Win8 menuing system, not VMware's Unity funtion ot the Win7 Guest's menuing system.