Mystery part from PM935-TS?

[kb58]

I'm going to feel real silly if that's it. Both R8 adaptors (drill chuck and collet holder) were purchased from PM at the same time as the mill. I looked down the bores of both and <shrug> they're threaded about half way down, with no giveaway as having been plugged by anything. Does anyone here have either R8 adaptor they can check to see if there's something down in there? It's a complete mystery to me, however, why such a threaded plug would decide to back out along with the draw bar, but who knows.