When doing a binary operation between one bitmap and another, you sometimes take a reference to the containers from the second bitmap and add them as-the-are (without cloning) to the first bitmap. E.g., look at https://github.com/fzandona/goroar/blob/master/roaringbitmap.go#L169

The net result is that you end up with containers that belong to two bitmaps. This means that modifications to one bitmap will magically propagate to the other bitmap. That is probably not the desired effect.

I believe you should clone containers before adding them to another bitmap.

(I can submit a test case, but it is a design issue that is present through the code, not a one-off bug.)