I have been playing a Beastlord Sovereign with a Familiar to help Tame beasts faster, but have noticed what may either be a new bug I hadn't previously noticed, or an extension of a still persistent very old bug I recall having reported way back in FE beta days.
Since a Familiar isn't considered a champion, I can't cast unit enchantments on it like "Mantle of Oceans" which greatly reduces the cost of tactical spells (including Tame) ... while my Familiar can cast every spell my Sovereign can, it doesn't benefit from the enchantments and thus its mana cost to cast a spell like Tame is much higher than my Sovereign when my Sovereign does have MoO.
However, I am frequently seeing this confused in tactical combat; I have seen the MoO tactical spell mana cost reduction disappear from my sovereign mysteriously in tactical combat (the tooltip indicates the spell would cost the same as it would without the MoO mana discount), and at least the tooltip for my Familiar indicate its mana cost for casting the spell is reduced the same as my Sovereign with MoO (when I don't believe its supposed to get the discount since the Familiar cannot have a unit enchantment like MoO). This extends to the spell getting disabled on my Sovereign (with MoO supposedly enchanted on the Sov) when it could be afforded from the mana pool with the MoO discount due to 'insufficient mana' (but, again, there is sufficient mana if MoO were taken into consideration).
I have also noticed if my Sovereign casts Tame, even if I have enough mana to cast it again from my Familiar without MoO, the spell disables on my Familiar but no reason is indicated in the tooltip. I wonder if my sovereign's cooldown for Tame is being applied to the Familiar as well (even though the Familiar hadn't cast it) ... if that is the case, even if that is intended, it would still be helpful if the mouseover tooltip for the disabled spell would indicate it is disabled due to cooldown (and I doubt a cooldown triggered by a Sovereign casting a spell like Tame should inititate a spell cooldown on a Familiar when the Familiar had not actually cast the spell).
This might be related to a very old bug (from back in the FE beta days, I think it may even have been present in WoM) of tactical spell mouseover tooltips not updating such as the cooldown timer for spells with a cooldown like Tame. Tactical turn after tactical turn, the Tame tactical spell mouseover tooltip will report the same number of cooldown turns for the spell (that is, it will report 9 turns remaining on cooldown, and the next tactical turn for the unit it will still indicate 9 turns remaining, and the next tactical turn after that as well, etc.) The tooltip will seemingly only actually update if the actual cooldown expires (it will indeed take the 10 proper turns), or if another spell is cast during the cooldown in which case the cooldown timer on the tooltip will update just that time (but won't update again until either another spell is cast, or the cooldown genuinely expires).