It could be.
I also saw that there might be internal problems in newer version WinDBG even without using VirtualKD.
Somebody said that with using newer version WinDBG, they couldn’t watch register window.
But with old version, they could watch it.
(http://social.msdn.microsoft.com/Forums/windowsdesktop/en-US/5eeee06e-8665-43e8-abd8-8c1f5f264022/windbg-61-issue-with-registers-window-when-debugging-virtual-machine?forum=windbg)