After starting recordmydesktop and clicking 'record' the window with recordmydesktop disappears. And so I can not stop it. With Kazam I had the same problem.
I installed the program as root and use it as a user with limited rights.
The recordmydesktop window disappears completely. It disappears from the taskbar also.
have you had a look at the taskbar (or whatever this is called in Ubuntu)? I mean the place at the top right of your desktop, where you also have access to sound, power options and so on. Once you start recording, a small red icon appears (on the unity desktop). Clicking this, you can choose to pause or stop the recording.