I have just started 30-day OnDemand trial, enabled "Require JIRA issue key for a successful commit" yesterday and still one can commit changesets with any comments.
I tried to raise a support ticket but it looks like I don't have permission to do that (maybe some trial limitation, but it would be very ackward no to give any support during trial).
This is a known bug at the moment: JST-5503
In the meantime, you can contact Support and we can get it working again for you. There is no restriction on who can submit support requests, but you do need to sign up at support.atlassian.com to create a user account for yourself first (that account is not shared with other Atlassian systems).