Patch to resolve some issues.
I just tried this and a project saved in r164 could successfully be opened in r164.2. If you encounter problems please file a bug following all the guidelines - as demonstrated here we can rarely solve a problem from a single comment alone.
Just for Ashley's and Rory's information, I also loaded up a project and got the error "project saved with future release" after updating to 164.2, but reloading the page again fixed this.