While I'm sure, and hoping, many are not running trunk and the new client together.
There was a problem with a function call, and this should now be fixed. It also fixed a potential mac address problem causing pretty much the same thing.
Please upgrade immediately. While I realize some of you have lost hosts, you really haven't. The hosts disappeared because, this bad function, the primary mac address was being deleted from the database. The names are still present. I recommend, if possible, just trying to re-register the hosts.
I know this isn't always viable, and I am extremely sorry for the oversight, especially for the length of time this has been going on for.