I've noticed this as well. It doesn't appear to be related to IPv4 vs. IPv6; it appears to return whichever entry is first in /etc/hosts.

Agreed. I just posted my workaround as a minimal fix to highlight the issue: accessing $? after another command was ran (which can be easy to miss).

I noticed this as well. The issue is expecting $? to refer to the exit code of minisign -V when it's actually referring to the exit code of the if [ -f ${filename}.asc ]; block which will always be 0.