Test was failing again after the update. However, when boundary_mode='ignore' was included in line 283 of starfield.py, the tests passed with flying colors.
The Getting Started page in the documentation is now out of date. It's no longer a future thing; you can run pip install remove-starfield now. I don't know what else you want on this page besides this instruction though (or I would've just updated it).
We were testing your starfield removal code and realized that when you adaptively reproject an image with an identity conversion, i.e. from the original WCS back to the original WCS, you get an edge of nans. Note that when you use reproject_interp this isn't a problem; there are no nans.