Yes that is the rule you get the partial action immediately I've always felt that this made the spell "inherently quickened" which means that if you had to wait a round it would be a level -1 spell. So either haste is out of wack or quicken is. It also removes a large part of the incentive to quicken spells of 4th or 5th level when a quickened haste works will accomplish the same thing at a lower level.
In my opinion haste sort of represents a spot where the rules break down, kind of like the universe and a black hole.