They are stealing, yes. One day in a week, they pick around 33% of your hashrate. Today is that day for example. Tomorrow, we must be earning normal again...
Today I am earning nicely on there, thats what worries me, its totally random. Hash refinery and Zpool is pretty much same each day.
Maybe they pick not all miners at once for that specific day...maybe they pick some miners coincidentally for that low-erning-day.
My experience so far is, that one day in a week, my earnings are around 33% lower then the rest of the week.
EDIT: What is more rewarding in your experience: Ahashpool, Refinery or Zpool?