Re-routing with loops

[comqpq]

Over several years and different OSMAND versions on different phones, I've occasionally been given routes with loops in - I think they were all after deviating and being re-routed and possibly all with an intermediate destination. On one occasion I was told to take the 6th exit of a 4 exit roundabout! Anyway, this time, I took a screenshot.
I started to the west of the shot, and deviated slightly to a fuel station at the left end of the looped route you can see. After coming back on route and continuing along the road (A30 in Cornwall, UK) I saw that something strange was happening. Zooming out showed me the screen you see. It looks as though it wanted me to drive to the intermediate destination, then fly in a straight line back to where it re-routed and then go to the destination, maybe doing another straight-line hop from intermediate back to the A30.
There seems to be a significant fault in the routing (or re-routing) algorithm for these things to happen. Anybody else seen this? Any idea what it is in the algorithm that causes it?

This time it was on OSMAND 3.9.10 released 2021-03-01 on Android 9 on a Motorola Moto G(6).