This is for the shulker box container. For the shulker mob see MCPE-41736 (in short, shulker < shulker box < full block).

Steps to reproduce

1. Place dark shulker boxes against a light background (for contrast).

Observed results

You can see a gap between two shulker boxes, and pretty much between a shulker box and a block. You cannot actually hit through the gap, as far as I can tell.

Expected results

No gap. Closed shulker boxes are exactly one block wide.