I just bought my nexus 4 like 4 days ago, my last phone was Samsung Galaxy Ace. So Nexus 4 has 2 GB ram, but when i do heavy multitasking, then i close the apps it went from 500ram used to 700, next day to 900 and next day to 1.3gb ram used without any apps running. I rebooted it and now its barely using 400 with facebook and skype running. Why does this happen?