Glyphs treating intersecting paths as open corners

I am experimenting with an idea to create a typeface somewhat resembling twisting strips. Because of that there is a lot of paths that intersect with themselves.
That caused a problem that I am not sure how to solve.

In letters like “a” on the screenshot I want that overlapping part of the letter to be its white inside. But Glyphs refuses to make it white, my guess is that it treats it like an open corner.
Is there a way to solve this problem without redoing the inside manually as another path?

Dangerous because it is an edge case for a renderer. And you may end up with different results in different environments.

Two ways:

  1. do not remove overlaps at export (do your own overlap removal) and test as much as you can in different apps and sizes.

  2. or split the path at the intersections and keep it open manually.

I would probably prefer to do the latter.