Not showing file difference in apk

This bug was originally reported by Marcus Hoffmann (bubu@bubu1.eu) in Debian bug #916359:

When comparing both attached apk files diffoscope never shows that the
resources.arsc file contained in both apks are different. It also never
mentions those files in the --debug output.
Manually extracting the apks and running diffoscope again on the
differing resources.arsc files produces a hex-diff output.