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
Test.zip (2.7 KB)

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