sleep mode is generally tricky, because it is a playtogether of software and hardware, both must work.
so software telling to sleep, and hardware needs to savely park all components before pulling the current,
those control cycles are on non apple hardware sometimes not closed, because we have a faked smc,
pretending to store data, and apple strenghtened the security processes step by step ( SL, Lion, ML)
sometimes their own hardware cannot follow their rules.