Thanks for the response. I thought it was a bug because some guys with their roms consider it as an issue but idk why after what you have told me? So tell me when it's a bug?Nope... it's a state to where the device "goes" after a certain amount of inactivity in order to save battery, turning off all that is not necessary... keeping the minimum working so you can receive calls, sms and (i'm not sure about this) pushing notifications.
It's not a bug... it's a good thing when works correctly, when it come to enter into it and getting off
ps. Forgive my english