It's not a bug in Parallels or VMWare's code. Any application that includes certain frameworks (like OpenGL), triggers the change. That's Apples poor architecture, and the vendors have no control over it.
Since both applications support accelerated graphics, they use that code, and therefore trigger the change.
This is a broad issue, resulting in much much worse battery life in the real world than on the mid-2009 machines.
For the record, the
** in my post above is not profanity. Evidently the censors don't like that word, which is also used to describe the movement of liquid up a straw into your mouth. It rhymes with a profane word, but that's not the one I used!