Slitherine

One of my cavalry units had only one possible tile to move and it was a tile not adjacent to it.

Screens from two different angles.

https://i.imgur.com/fvkzI5d.jpg

Before in the same turn I engaged an enemy (blue) adjacent infantry unit with my other cavalry units to unpin my cavalry unit (that one I wanted to move). Maybe it was the case.
Is it even a bug or some feature?

I must admit I am struggling to see the reason for the situation in this particular example.

If anything like this happens again, please save the game and attach a copy here, so that we can take a closer look at what is going on.