Path of the Mage uses this code for mana spell cost reduction:

            <GameModifier>
                <ModType>Unit</ModType>
                <Attribute>AdjustUnitStat</Attribute>
                <StrVal>UnitStat_TacticalSpellManaCost_Multiplier</StrVal>
                <Value>-0.25</Value>
                <Provides>-25% mana cost for tactical spells</Provides>
            </GameModifier>

I picked the path of the Ninja (a custom path) for the Avatar of Justice, a custom spirit hero from OtherWorldlyAllies mod, and in the first battle after I chose Path of the Ninja, the Haste tactical spell actually cost 128 mana, and the other spells were more, when I used this same code.  Has something changed recently?  (I mean, loads of people would have used the Mage Path, and we haven't had the problem of multiplying mana cost being reported).

There are no conflicting files in my Mods directory AFAIK.  In my latest games, I have been using Slow from Water Adept by a Mage hero and it worked fine.  I wonder if this is a once-off bug?  I'll check.

EDIT: No, it happened again in the same battle.

Any ideas?