HB JRRT!

[vates]

For a moment I wondered if it was some kind of mod to improve the smoke.

Perhaps it probably was.
I saw our local team who prepared for the pipe smokers World Cup honed this technique.
I'm not into pipe "sport", this is a meditation and leisure activity for me, so I never bothered to actually clear this thing up.

 

[Casual]

Those guys were intellectuals. They didn't know how to clean their pipes.

I’m betting you’re right. Smoke a pipe all day and maybe the mortise swells and the stem gets tight.