Inpainting doesn't work with A1111

I'm not able to get inpainting to work correctly. Is there a guide for configuration that can be added to the readme or is it possible the feature is broken?

Using a normal checkpoint: it generates an entirely separate image with the selection area becoming a mask
using an inpainting checkpoint: it generates flat gray, every time.

I expect it's user error but I can't find any information on this for the plugin.