[Q] 4G always on! topic

Hi. On my gm-g900i (australian) s5 i have the latest XtreStoLite installed with the correct bootloader & modem.
For some reason at all times it shows 4g in the status bar, even when i am not in an app that requires internet. It will only drop to 3g when i am in a poor signal area.
Why does this not dynamically change based on apps used, as it did in kit kat? Have i done something wrong? I am after the power saving of 3g for background data, then 4g when using an app like facebook, chrome etc. This was automatic before?

thanks in advance.