This was reported to Debian at;

https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=435901

I've confirmed it still happens with v2.0.2 in Debian testing now.

This should not be happening. It's unlikely to cause any corruption (which would require a strong-sum collision), but it might be indicating a rollsum bug that could be causing delta calculation to miss some matches, resulting in a larger delta than it should.

I will investigate.