Environment: Arch Linux, xorg-server, i3-wm, slock Steps to reproduce: 1) Rotate the display: $ xrandr --output HDMI1 --rotate left 2) Lock the screen: $ slock 3) Unplug your monitor video cable from your computer. 4) Plug your monitor video cable back into your computer. 5) The screen is still locked, but the right side of the screen (when horizontal, the "bottom" if rotated) is unmasked.
The unmasked content appears to be live, as my clock was updating. The "mask" seems to become un-rotated when the monitor is being re-initialized. Rob