I've made about .01% of the number of shafts any one of these guys have, but i have studied and thought hard about the issues of capped ferules for myself.
I don't think the thin air gap is a problem. (assuming this is not a jump/break) Or if that was the problem, i think the ferule would have failed differently with more failure at the threaded glue joint. & more of a cross-ways crack around that location (which is not apparent at all.) The joint does not seem degraded or loose in any way (from the pic) so there is/was a lot of integrity in the making of it. The cap is thick. Whatever caused it to fail must have taken a crescent moon bite out of the tip, as well.
Depending on the material, it is faintly possible it was too tight for the tenon, screwed onto a very dry shaft with a barrel wrench equivalent, and later the wood got humid and swelled. This is way out in la-la land, but might be what happened if there is no tattle-tale damage whatsoever to the leather tip itself.
As others have said, air gap may cause it to feel different, and certainly different than a through tenon. Just don't think it was the failure cause.
There are "air gaps" in most of my shafts because they are hollow. The wood goes right up to an internal collar, though. Then again, other than myself, only 4 other people use them, so my statistical base is not particularly robust.
smt
specially when dealing with short ferrules.
