The current version of grep was published on 2016-02-18 which could be around when sbuild broke for me. Did not notice immediately as I was working on something so I used the chroots directly (which works as there I have a UTF-8 setting there which sbuild deliberately drops).
I downgraded grep in my chroot to 2.22-1ubuntu2 and that causes the issue to go away. So it is definitely the new version of grep in my environment.
The current version of grep was published on 2016-02-18 which could be around when sbuild broke for me. Did not notice immediately as I was working on something so I used the chroots directly (which works as there I have a UTF-8 setting there which sbuild deliberately drops).
I downgraded grep in my chroot to 2.22-1ubuntu2 and that causes the issue to go away. So it is definitely the new version of grep in my environment.