I was just over on the notubes website trying to do a bit of research when I found this:
given that we now know Gee was running a DT rim, this sounds exactly like what happened to him.... link"When running a tubeless system some of these standards are not safe. If the drop channel is too deep the tire will fit
loose while uninflated. This loose fit will make inflating tubeless very difficult, but of greater concern is safety. If you get
a large cut in a tire while riding, the tire will deflate rapidly and, because it is a loose fit, may work its way off the rim
before you come to a complete stop which will drastically impair handling. BST rims and other rims designed for tubeless
use will have a shallower drop channel to prevent this."