First, I said it was wedged up in there... not that wedges were used to hold it up in there.

All this would have required is the stone have a couple bumps sticking out the sides that made it especially hard to push up into place "straight" (flush with the roof of the DP).

It would not surprise me if Mamun did knock the piece out while examining the entire passage for secret doors and such. Having found it, possibly by simply banging on the walls looking for hidden chambers, he then realized he had found one. Rather than trying to dig up (which would have been a suicide mission) he backed out of the pyramid, found a spot level with the plugstones, and started removing blocks to get in to that specific area.

It's possible that the report of Mamun's workers hearing the stone fall was more like the workers were banging along inside looking for secret passages when they hit on the fake block, knocked it loose (just like they're supposed to have) and it was Mamun outside the pyramid who heard the stone crash and knew it was something important. They then started digging the tunnel towards the spot where the stone had come down (meaning they started outside the pyramid and headed towards the plugstones), and that has given rise to the malformed mutation of a story we have today.

That story makes a ton more sense than the one we've been handed via oral tradition, now that we know the facts of the layout of the pyramid.

Anthony

You can lead a horse to water but you can't make him think.