In an earlier version regeneration effected health and mana, but it was a relatively small effect for health (a regeneration of 1 was much better than 0, but you would have to get regeneration up to about 90 to double the rate of it at 1). I believe mana regeneration was percentage based rather than a fixed amount per time unit, so unless they changed things in recent patches, that may be the effect you are seeing with a higher intelligence.
