Still no word on the official RAW answer, but I have asked in two different places (wizards and paizo).
Something I did want to comment on, and perhaps this is just because I'm a lawyer and so I'm used to having to deal with applying written rules to situations that were not originally contemplated when the rules were written.
It is clear that the original RAW did not contemplate the effects of haste on zombies - or rather, if they did, perhaps they did not need to say much because haste, as it was written (and at the same times zombies were written) gave an extra action, so nothing needed to be said. Thus, 3.0 is born.
Then through playtesting, it was discovered that giving an extra action causes problems where spellcasters are concerned, so they nerf haste to "fix" that. Probably at the time NOBODY was thinking about zombies and the implications it would have for hasting them - so even if they contemplated zombies originally, that original contemplation was turned ambiguous by the change in haste done for entirely different reasons.
In other words, the way things worked before, it was simple and straighforward - add or subtract actions for slow, zombies, haste, etc. But then they decided adding actions that allowed spellcasters to cast two spells in a round was "broken" so in an attempt to "fix" that they made a change without contemplating the ambiguity and lack of clarity that would create.
That's just a hypothetical - I have no idea what the designers were thinking when the rules were written and rewritten. Only they know. Only the rules writers/arbiters can really answer my question.
And again, perhaps this is just because I'm a lawyer and so my brain is rewired wrong, but what normally happens when you have a rule that appears not to have contemplated a particular scenario is that you have to judicially resolve the ambiguity. Sometimes the resolutions make so much sense that legislatures just leave them alone because they are good rules to use. Sometimes they make so much sense that legislatures pass new laws specifically to codify the judicial rule. And on occasion, the legislature says no, you got that wrong, here's what we REALLY meant and they pass laws that explicitly cover the situation, but with a different rule.
I suppose in this case we are appealing for the judicial ruling from the rules arbiters. And if there is an errata on this for haste, that makes it the legislature acting, though really, they are the same body in this case.
