The hotbar always switches to the first slot after leaving the world. I had cobblestone in my first slot and an iron axe in my 7th slot. When exiting my world, i had selected the 7th slot. But when rentering my world, it had selected the first slot.
Linked issues
Comments 4
Duplicate of MCPE-7987, which was resolved by @unknown as working as intended.
My device is a samsung galaxy note 2 gt n7100.