I have a fresh installation of Kubuntu 14.04. If my usb mouse is connected during restart, as soon as the mouse is moved after restart, both, touchpad and mouse, start malfunctioning. The cursor is still moveable but especially the left klick isnt recognized (not entirely correct: i can open the main menu for example but cant open any applications afterwards, the right click seems to work however) . If the mouse is connected but not moved the touchpad works fine. The only solution so far is unplugging and replugging the mouse (at every reboot).
Edit: The bug occurs also with gnome and xfce and even during installation processes.
Edit2: A workaround is clicking the right button first and the left afterwards on the desktop. This however lasts only until the next left action is done. The replugging solution is stable.