For anyone following this, I had a reply on the repo bug ticket saying:

> I just downloaded nginx_1.7.8-1+utopic1.debian.tar.gz sources from PPA and it looks that unfortunately it doesn't use the latest version of the module. Please contact PPA package maintainer (teward) and ask him to update it.

So, I've just done that - I'll let you know what the outcome is - thanks!