Comment 1 for bug 1483923

I'm going to take a wild guess that the issue is because vivid's nginx-common.postinst has this line:

invoke-rc.d nginx start || exit $?

Which will make postinst fail if nginx fails to start for the first time.

15.04:

http://bazaar.launchpad.net/~ubuntu-branches/ubuntu/vivid/nginx/vivid/view/head:/debian/nginx-core.postinst

14.04 did not have this behaviour:

http://bazaar.launchpad.net/~ubuntu-branches/ubuntu/trusty/nginx/trusty/view/head:/debian/nginx-common.postinst