I installed Xournal today too, and I think I see the same behavior: If you start xournal, it'll start in "Pen Mode" for writing. Then if you try to switch to something different, lets say erasor, it'll just ignore the switch and stay in "Pen Mode". It doesn't make a difference if you try to switch using the icon bar or the menu. I already tried to uninstall, remove ~/.xournal and reinstall (had it installed som time ago, so I thought there might be some problem with the config) but didn't help. Any hint for a solution or a way to debug further would be welcome.