This is a small performance related patch, to try to address a report that we received on poor performance in some situations.
Although we were unable to duplicate the issue, we believe that it was likely virtual shadow map related, and have made some tweaks which we hope will address the issue.
If anyone experiences any odd or transient performance related issues, please do let us know about it on the forums. Especially if you can recall anything leading up to when they occurred, as this information can help aid in narrowing down the possible causes.