I had this issue too before the expansion. Try not to switch off cleric in the middle of an animation of another spell. For instance, do not lustrate/eye for an eye/virus/indomitability/deployment tactics and a long etc of instant SCH casts and then in the same 0.2 seconds switch off cleric, because many times it won't work, give it at least a half of a second before you attempt to disable cleric, if you do it all at the same time there will be many times where it won't work.