Hmmm... Not recently, but there is no reason that it shouldn't work, although downgrading has been a little tricky.
If you are having issues, return it to the previous software load, default the database, downgrade and verify everything is working properly, load the proper license key, and then restore the converted database and all should be fine. I don't recall anything in the release notes noting downgrading issues, but then again I don't always read them completely. :/
If things get real hairy, I would just call tech support and have them work you through it.