If you dismount a cavalry unit (Armored Noble Lancers in this case) during the deployment, you no longer can remove it from the battlefield to get the points back (even if you re-mount them again).
As you can see, two Lancer units don't have a square highlight that indicates them as removable, but also are not "mandatory" units.
Annoying that that one got through beta. We will look into fixing it for the next update.
For technical reasons the solution may have to be to disallow mounting/dismounting in the force selection phase, and only allow it in the subsequent deployment phase.