If you stand ontop of a shulker box and shift click onto the box with another box still allows the player to place a shulker box.
Linked issues
is duplicated by 6
MC-107473
You can place Shulker Boxes underneath yourself
Resolved
MC-107516
ShulkerBoxStacking
Resolved
MC-107523
You can place Shulker Boxes where you're standing (inside the player)
Resolved
MC-107527
Makes a ridable mob glitch up a block
Resolved
MC-107628
Shulker Boxes Displacing Entities
Resolved
1 more links
Confirmed in 16w39a