Welcome to the forum.
I think you are doing something different than you think you are.
To check open a new document (file/new). Draw a black square with the paint brush then erase a section as above. Think you will just see erased section.
Do you have eraser in brush mode (box in eraser tool bar)?
Do you really have a white canvas with a black line?
Thank you, everyone.
You seem to have nailed it. Is there a way to default to this? Or should I do this to every layer?
Can I draw a square, for example, without using a "stroke layer"? If I turn stroke off, the square goes away.
You can use the rectangular marquee tool to draw a square and then go to Edit>Stroke, but you loose the ability of easily changing your edits.
You could also save a layer style and use that with shape layers (or any layer), but you would still have to add a layer mask unless you recorded an action.