Hey, I received a Sony Z2 for my birthday. Great phone, but I am a little confused by the 'stamina mode'. So I get that it saves power by turning it on but when you go into its setting under the tab 'activation' it allows you to use the slider to select a percentage to presumably set it to when you want it to activate stamina mode. This seems to actually do nothing, you can still turn stamina mode on and off, no matter what I put the slider to it won't change when stamina mode is on. I thought that the purpose of it would allow me to choose when stamina mode become active? Any help?