They’ve wrapped it up nicely in this Youtube video which servers as both a demonstration and tutorial.

For detailed information on how to repeat it and how it works check out their discussion forum and get “bumping”!

In comparison to the fully loaded sector when the door is missing the following applies:

3 areas used as the SI supply drops are now open (not just the 1 originally discovered).
The grunts and turrets are not loaded in one of the circular areas.
Adverts for cars are missing from the walls.
Various items are not loaded such as the Opticon health dispensers and stand alone terminals (such as the one near the shotgun).

So it’s a case of good work on finding a glitch, now can we do this on other sectors to access even more areas that should be blocked off?

JSM26 has uploaded an ODST video to his Bungie.net file share showing missing Opticon dispensers and de-loaded doors in the starting sector. Further evidence that the ODST modified Halo 3 engine has glitches, possibly exploitable to access other blocked off areas the designers never wanted us to get to…