It's definitely not just when over 4.2 GB RAM is utilized, I see this bug happening any given time; it's completely not understood right now by me. Definitely it will never stay in sleep mode anytime over 4.2 GB RAM is utilized ever not the first, second, third, or ever time that I have tested. I am now using a new BIOS/firmware and I see that piece remains.
Additionally it commonly wakes back up under 4.2 GB RAM utilization, in that case it does complete the sleep mode once invoked the second time.