When opening a shulker boxes that is placed sideways, one block away from a chest (and the shulker box should open in direction of the chest), you'll occasionally be put on top of the chest
The GIF I tried to put into the attachments is too large (10 MB isn't a whole lot though!). So here it is: https://imgur.com/Y0Jmqqc
Can confirm. Most likely intended since you don't quite fit into the gap between the open shulker box and the chest. (Player is roughly 10 pixels wide, the gap is only 9 pixels wide)