Shulker Machines in Market are THIEVES!!!

[AlyCatMeow]

I lost a shulker in the market just now whilst using a shulker machine. When I pressed the button to extend the piston to break the shulker, the box vanished. My inventory was not full. It did not despawn. I watched it float there, ready to be picked up. When I moved towards it, it vanished... I relogged, thinking it was probably a ghost block and that didn't yield any better results. I checked the dispenser as well and it wasn't in there. And it definitely was not in my inventory... I checked everything extensively before coming to post here.
This happened at -76 80 189 facing west. It's the shulker machine in my shop.
The shulker in question was undyed, unnamed, and empty. Previously, it was full (sans one slot) of gunpowder, which I emptied and placed in a chest as an item for sale in my shop.
I am not overly concerned about this particular shulker box being retrieved and returned to me as it was empty. I just wanted to make the problem known. I would hate to see anyone lose something valuable due to this issue. Maybe it's some kind of bug?
I tried to give thorough details but I'm ready to answer any questions if need be.

[Dax23333]

I've had a look at the shulker machine in question and while I have not had any of my 'shulker boxes' (pumpkins) vanish yet they have been dancing around a bit while the piston is extended. The more open shulker machines this does not happen, which suggests to me it was either flung out or pushed into the wall. Could this have been the case?

Unless anyone else has any ideas what could have happened, we could automate some testing of this to see which designs are most or least safe over many many cycles. This is the first i've heard of this.

[Forseth]

Not sure If it's relevant, but they've updated the floating item mechanics in 1.13 (or maybe 1.13.2).

[SwayLight]

Pistons pushing shulkers when there is blocks around the places the shulker can land will often cause a couple of things to happen, 1. The shulker gets stuck in a wall and you just walk and pick up. 2. the shulker is turned invisible (had this happen once).