Strange Boolean subtract bug?

I have a strange “bug” with an old typeface. I like to cut out a rectangle out of 8. With the rectangle selected I click on subtract path and ALL paths are deleted.
I reversed all paths and tried different path directions for every path but the “bug” is still there.

If I move the rectangle upwards, so that only two paths of the 8 are in the cut-out area, the 8 will be cropped correctly.

This “bug” seems only be present in the actual Glyphs file. Tried it out on other fonts and it’s working like a charm. So, what is wrong with me?

If you wanna test on your own, Glyphs file is attached.

Thanks in advance,
Thomas (2.7 KB)

Move the rect up one unit. This is a known bug.