When I open an image in Krita, the brush set to my pen tip is the one I was using during the last session. However Krita does not remember the eraser, and it automatically sets it to whatever the pen is using. Is there a way to remember the eraser setting separately?

I'm using a Surface Pro 2.

Only by coding that feature . I'm sort of collecting a list of things that should be remembered between sessions and have started on tool settings, fg/bg color, opacity and flow, but eraser mode makes a good addition. Not sure whether that code will land in 2.9, though.