>TT
>NN
>TT
>NN
>TT

T=Trapped chest
N=Normal chest
>=Hopper pointed at chest

Depending on the direction and the coordinates, placing an item in one of the hoppers will result in the items being placed on the second half of an adjacent double chest, or simply deleted.

This is probably due to a conflict between the new double-chest/hoppers and rules their natural behaviors.