I've seen the small reed switches that are supposed to detect when you close a notebook screen be defective present a permanently closed circuit. Putting one of those in your bomb would be very bad.
The Palestinians seem to blow themselves up by accident on a fairly regular basis and they have a lot of experience with these devices.
Even the angle the device was held at could be deadly with some types of triggers if the switch were inadvertently turned on. He would not have had to be removing it, only jostled the contents of the pack wrong and turned the switch on on one of the devices.