I reverted to an older version of WIN X last night and I still couldn't get my extended screen to work.
Suddenly today it does again, it's a bit odd.
I didn't do anything different, it just suddenly works again.
And I even did reboot and try a few things out after going back to 10525.
Some of the things going on the background seem weird even if I do like it overall.
The newer version was even working fine awhile.