Amateur tape
I read that the tape found originally contained footage of the helicopter parts that the Taliban was bragging about a few weeks back. The bin Laden footage occupied the last part of this same tape, and then the taper rewound the tape and recorded the last part of the bin Laden footage over the top of some of the helicopter footage.
Sounds like an amateur job to me, maybe someone who was informally assigned to shoot footage to be used in eventual propaganda.