/etc/apt/sources.list gets modified

I have two, nearly identical kali systems, except for the obvious differences: one on an old MacBookAir, the other on a RasPi 4/8GB

On the RasPi, for unknown reasons and with no (so far) discernible pattern, the /etc/apt/sources.list file gets modified. The way it normally looks is as follows:

Code:

---

deb http://http.kali.org/kali kali-rolling main non-free contrib
deb-src http://http.kali.org/kali kali-rolling main non-free contrib

---

but seemingly randomly this gets changed into:

Code:

---

deb http://http.kali.org/kali bullseye main non-free contrib
deb-src http://http.kali.org/kali bullseye main non-free contrib

---

which of course doesn't exist.

So some package seems to be misbehaving, updating the sources, assuming (falsely) that we're on regular Debian, but I'm not quite sure what. Anyone seen this before?