Demi Human in 3.5 b4 w/ Archmage Hero

When I was playing DemiHuman, I decided to get archmage hero for the mana regen. Unfortunately it seems that all mana using units have some cooldown on their skills (medicine man, tauren/bigfoot), which makes mana regen obsolete. I am wondering if there is a skill cd on mana units that is sychron with the time they need to regen full mana.
Tell me if you experienced similar unit behavior while casting spells.

Ramalamading aka Seeraeubaer