My guess is the reason is systemd's enabling quota before our service is enabled. Can you please check in journalctl if that's the case? You should have entries there that talk about enabling quotas before quota.service is run, if at all.
This needs to be fixed asap, but the question is how as systemd offers features, like automatic on demand checking when a device is connected, that the quota package doesn't have, while systemd lacks other features, like quota's creation of quota files and check only when not clean unmounted. This information is pre-Jessie so it might have changed but you get the gist. Michael -- Michael Meskes Michael at Fam-Meskes dot De, Michael at Meskes dot (De|Com|Net|Org) Meskes at (Debian|Postgresql) dot Org Jabber: michael at xmpp dot meskes dot org VfL Borussia! Força Barça! Go SF 49ers! Use Debian GNU/Linux, PostgreSQL