Hi @dan-brown_0128,
I've done some more research on this, and per the spec we definitely should not be url encoding anything in the Filename field: https://wiki.debian.org/DebianRepository/Format#Filename
I've filed this as PG-2591. It's an easy change, so we'll include it in this week's release on Friday. It still is strange that I couldn't reproduce this, but hopefully this will resolve the issue for you and anyone else that is seeing this.