Please elaborate, mabye post some screenshots.
It also doesn't appear to be actually /doing/ a mask either,
A Mask of what do you expect it to be »doing«?
It provides a kind of temporary method for editing Selections as Channels.
By "doing" in this case, creating the customary red space in which to paint a mask (negate or otherwise).
There's nothing to screen-shot, it just seems to randomly happen when I open a quick-mask and it doesn't work. I have plenty of RAM in my system.
I've not been able to duplicate it consistently, unfortunately - it just happens randomly.
There's nothing to screen-shot,
I stand by my request.
it won't paint in the mask (default = red).
A screenshot might show which Blend Mode the Brush is set to etc.
There's nothing to screen-shot, it just seems to randomly happen when I open a quick-mask and it doesn't work.
Do you trigger it via keyboard shortcut or the button in the Toolbox?