It's a bug in the software, will be fixed shortly. I mentioned this in a few threads. There's a few other things broke too such as the pop up for new pm's, smilie box disappears when you click on it. Probaly about a hundred other things
No kidding, this is not a "gold" release and I wouldn't even be using it at this time except I installed it as last ditch effort to drop the CPU usage on old host. There's no convversion script to go back to phpbb2. The next release however is expected to be gold and suitable for production use, I will also note that this software underwent a independent security audit with no major issues found. Small problems that were found have already been fix and applied. Most of the bugs are small problems like that.