If you scroll with the Jog/Shuttle against the begin of the movie you become the error message "Error Cannot go to previous keyframe"
If you close this message, the message returns a million times and you has to kill the avidemux3_qt4 process to come out.
Confirmed!
Same happens when you go passed the end with jog/shuttle!
Avidemux QT v2.6.0 (r8154) ubuntu 12.04.1 lts 64-bit.
I never use the jog/shuttle.