Screen full of random colors when starting Xorg with Intel Haswell HD Graphics P4600
I'm running the DragonFly 4.0 RC on an Intel Xeon(R) CPU E3-1245 v3 with HD Graphics P4600 (PCI vendor 8086, PCI Device 041a).
When starting Xorg using xinit or startx using either XFCE4 or KDE4 (my preferred DE) as session managers, the screen becomes full of colors that change randomly, almost with a rainbow effect. Absolutely no GUI elements are shown. No errors appear in the Xorg.0.log file. I've disabled acceleration in xorg.conf via NoAccel in the device section. I've also tried both the 2.21 and 2.99 versions of the Intel Xorg driver, with no change.
Please let me know what to do to help troubleshoot the issue and/or any additional information you may need.