Well, it also happens in the following cases:
- Selecting a DA with 1 chivalry unit
- Selecting an attacking army with 1 chivalry unit
- Attacking a defending army with 1 chivalry unit
Here's all 3 cases in one image:
Both the champion and knight are shown with 0 chivalry. So either it doesn't try to predict it or it does and isn't working.