0D24 detaches... from wrong end?

Here's a cool one I've never seen before. Savegame attached.

4D24 is called out of Didcot power station as usual, routed into the Goods, detaches the loco. All good so far.

Then...

0D24: "Waiting to depart but train 4D24 in front"
4D24: "Waiting for joining train 0D24"

To confirm my suspicion, opened up 0D24 and set its final order to be next, which is the post-runround join to 4D24. It joined up then took off towards Swindon without actually running the loco around!

I'm no timetable expert but I couldn't spot anything immediately wrong with the orders (it's just the default supplied TT with the re-release).

It's not the first 4xxx from the power station, 4D22 behaved normally. Anyone got a clue what just happened? Does the train change direction before executing the order to detach loco from front?