Here's the text of the added clause that was the last straw (the last of many other issues):
> Except as contained in this notice, the name of The XFree86 Project, Inc shall not be used in advertising or otherwise to promote the sale, use or other dealings in this Software without prior written authorization from The XFree86 Project, Inc.
How does that relate to copyleft? The GPL doesn't restrict anyone's ability to market the inclusion of GPL software.