On mac OS X 10.8.2: Open the GUI, Draw one place, Go to the simulator, Accept to upload the model to the server, Go back to the editor, A NullPointerException is now thrown and the GUI is from then unusable. This is both a problem in the 32bit and the 64bit version (run on a 64bit system) We also tested this on Linux Debian, where it does not seem to be a problem.