I'm afraid I don't know. Glad you found a fix though. It's entirely possible it's something that's a bug. You could look around in the Hibernate JIRA and see if anything turns up. That's how I finally found a workaround for an issue that's been driving me crazy for days.
Based on my (limited) experience with Informix though, it's possible it's something that's driver dependent. The standard ifxjdbc driver makes Java code break when you try to access views because it returns "bad" meta-data. It's also possible it's just a side-effect of Hibernate trying to (sort of) be all-inclusive and do at least some of what everyone wants rather than everything that some want. (I don't mean that in a bad way by the way. I agree with that sentiment for this project.)
(Link off to JIRA):
http://opensource.atlassian.com/project ... board.jspa