If the user is recruiting Gandalf with the faction Gondor, he is able to cast different spells.
While I played Gondor on the map Umbar, I used Gandalfs spell, where he casts it on a recruitment-building and the troop-building time is quicken to 75% (Sorry, I dont know the name of it right now, I think it was the second or third spell from him).
If Gandalf is far away from that building, he has to run towards it (since the range has a reach). If the user NOW uses another spell, meanwhile he is running towards that building (like using the spell where he gets on his horse), he will immediately stop for a short moment and then continue to walk towards the building.
The problem/bug is, that the player is now unable to control Gandalf. You neither can cancel his movement by clicking somewhere, nor is it possible to use/cast a different spell.