automake's mdate-sh script pretty-prints the modification time of a file. This output can influence further steps in the build process and make it unreproducible.
Something looking like autotools is capturing SHELL for use at runtime, which should probably be fixed to /bin/sh anyway. . Autotools also capturing the build path.
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).