Horizon seems to be interpreting "-1" (unlimited) quotas literally when tallying quotas, setting the 'available' field to 0 instead of infinity (probably because the expectation used to be that an unlimited quota would always be returned as None).
https://github.com/openstack/horizon/blob/master/openstack_dashboard/usage/quotas.py#L30 -- also checking for -1 when tallying unlimited quotas solves the problem.
The problem becomes more obvious in the context of ux improvements based on quotas such as https://bugs.launchpad.net/horizon/+bug/1033829, but it's also possible to check it by doing "nova quota-update --ram -1 <project_id>" then visit the project overview page: it will read "Used X MB of -1 MB Available RAM". It should be "Used X MB of inf MB Available RAM" -- although it would also be nice to display a nicer message when there are no limit!
Fix proposed to branch: master
Review: https:/