changing main screen after removing from dock

[Trecoist]

Why does the phone change home screen after being removed from the dock? For example it changes from clock screen to contacts screen. And I can't change them back unless I clear both of them and then add clock where contacts were and vice versa. Hope you understood what I meant

 

[Recon420]

There is a setting you check marked in the settings of the dock I believe it is something like after a certain amount of time unused return back to the most used app