Line of Sight
 

If I remember correctly, line of sight was never a requirement to complete a full cast of a spell. As it is right now, I begin casting a spell on mob, mob walks away in mid-cast behind an obstruction... spell fails. This does not seem era accurate.

Also while we are on the topic of LOS; PVP spells never required Line of Sight checks. I fondly recall "wall casting" many unsuspecting victims back on Rallos.