Can't stack custom tipped arrows.

When I give myself custom arrows I can shoot them normally, if I shoot them on the ground I can pick them up, but as I pick them up, they start stacking in a different slot and can't be stacked with the original given arrows.

I was using this:

/give @p tipped_arrow 64 0 {CustomPotionEffects:[{Id:20,Amplifier:0,Duration:330}]}