In message , James
Farrar writes

It *is* unusual to then run down the slow line to Hammersmith - I can't
remember ever being on a train that did that. Are there points between
Hammersmith and Barons Court that put the train back where it should
have been?

There are bi-directional crossovers between Piccadilly and District just
east of Hammersmith (at either end of the Piccadilly siding in the
middle of the track formation).

There was a time when early and late Piccadilly services would start
from / end at West Kensington (being stabled at Lillie Bridge
overnight), using District tracks for the most easterly part of the
route (and possibly right through to Acton Town). A few of these
services still ran as staff trains until about 15 years ago.

But I agree that it's rare to see Piccadilly trains on the district
tracks as far east as Hammersmith these days.

--
Paul Terry