The WoW wiki page on mana regeneration states Spirit does not affect in-combat mana regen:
Spirit regenerates high amounts of mana, but only out of combat.
InCombatManaRegen = 5% of Base Mana[per what?]
Spirit will be the primary modifier of mana regen while out-of-combat and only based on its affect to base-mana in-combat.
However, this directly conflicts with the in-game tooltip:
It's possible the tooltip was just never updated, but it's also possible the wiki was edited without real justification (There are no working sources for that page).
Has anyone done any Science™ or have a reliable source which explains how mana-regen works now?