Switching hands doesn't stack

In survival, I shot an arrow at the ground whilst I held the stack of the same arrow in my other hand. I picked up the arrow I shot, which went into a separate inventory slot. When I switched hands, the arrow still didn't stack with the rest of the stack until I did it manually. This doesn't occur with just arrows, but any block.

I'm not sure if this is intended, but it would make sense for items to stack when switching hands.