To quote Grom:
The sage also ruled no extra 5' step from a Haste.
Haste doesn't allow an extra step because you only get a single 5' step per round, and then only if you don't move at all otherwise. Once you took the 2nd 5' step, you've moved 10'. Its not a step anymore if you will.
The sage also ruled no extra 5' step from a Haste.