I've had this issue on my T450s with 15.04 MATE since March. I've also had the issue where the screen is completely black after resume and I need to change screens (Alt-Ctrl-F2, Alt-Ctrl-F7) to get the window manager back. This happens on external screens (Ultradock) and on the built-in screen. I will try UXA to see if that solves things.
I've had this issue on my T450s with 15.04 MATE since March. I've also had the issue where the screen is completely black after resume and I need to change screens (Alt-Ctrl-F2, Alt-Ctrl-F7) to get the window manager back. This happens on external screens (Ultradock) and on the built-in screen. I will try UXA to see if that solves things.