When one is using abilities that lower max mana, even if one is at the full capacity (reduced by any abilities), the option does not increase the maximum mana. Instead, it restores full mana. (My gnome necromancer was using dominate, which lowered maximum mana.)

Ah interesting!

Hmm, it works as expected for me, using both summon skeleton and dominate.

To be fair, I did not check the numbers--just the message text. I'll see if it recurs.