I'm on Windows 10 and I have my main monitor in landscape, 1920x1080 and another monitor to it's left in Portrait orientation 1024x1280, and an Oculus Rift CV1 connected to the HDMI out of the same graphics card, in case that detail helps - it's services are off when this happened. No hardware or software changes lately except the VA update, but I've not tried this before so not sure if it's a new issue or not noticed before.
When I move the Edit a Command window over to the left "tall" portrait monitor, and resize it, I get odd mouse behavior along the top and bottom.
The mouse-over tip on the lower and upper horizontal window borders is the right (\) angled double arrow normally used to move the bottom right corner of a window anywhere and never changes, and it's behavior is locked to that movement of resizing from the bottom right corner at any point on the bottom or top borders (left corners, center, right corners).