Unknown non-determinism added by this tool that turns files into Python. (PNG metadata? Ordering?) . Untested patch here: https://gist.github.com/lamby/d86fc228ae00733f1705b4ef80a5d7bb/raw
Our notes about issues affecting packages are stored in notes.git and are targeted at packages in Debian in 'unstable/amd64' (unless they say otherwise).