I don't know anything about primedice, what I know they're on the same owner.

However compared to site and situation, seem like is clear (One-month statistic) is playing a big role. In-stake you're on a winning situation during this monthly claim, and get less rather than previous month while in this month has a huge wagering.

But, in primedice you got more money with a less wagering amount comparing to stake.
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Anyway, is crazy so see your betting activity and losses. My advise, please try to control your gambling activity as the fellow bitcointalk community.