XMonad bug report

A consistently reproducible problem involving titlebar decorations & screenlockers. I would have submitted an issue, but I'm not sure if this is an XMonad core issue, an X.L.NoFrillsDecoration issue, a general decoration issue, etc.

Summary:
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Screenlocker (tested with various) is obscured by windows after display change when using a minimal layout with titlebar decorations.

Dotfiles:
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Gist of very basic XMonad config I put together to test this.
https://gist.github.com/altercation/1e5150369b4eb6f7caf013550de0bd43

Environment:
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Dual monitor (laptop/external), normally used one at a time. I have a udev rule that triggers a shell script that switches display when hotplugging/unplugging.

Scenario:
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1. External monitor active, internal inactive (or vice versa, point being only one display active)

2. Screen lock using any of several commonly used screen lockers (xscreensaver, i3lock, sxlock) is activated while connected to external display. Hot-unplug of external display triggers udev xrandr script, internal laptop display is successfully activated.

3. If using layout without titlebar decorations, there is no problem

4 If using X.L.NoFrillsDecoration to make title bar decorations on the windows, the layout windows are drawn on TOP of the screen locker on the new display. The screenlocker retains input focus, so it can be unlocked, but it is obscured by the windows on top of it. (I can see the screenlocker through the terminals since I'm using transparency, but if a non transparent window, the screenlocker is completely obscured).