Comparing an unsigned and a signed buildinfo file returns a hex diff

This bug was originally reported by Paul Wise (pabs@debian.org) in Debian bug #960814:

Package: diffoscope
Version: 144
Severity: minor

When I compare the attached files (one unsigned buildinfo file, one
signed buildinfo file) I get a hex diff. When I strip away the
signature, the comparison is a text diff as normal. The optimal
comparison would be to compare the missing container with the signed
container and then within that compare the two buildinfo files.

The same issue applies to comparing a text file with a tarball
containing the same text file, so I'm assuming diffoscope cannot yet
compare files across container boundaries?