Minecraft Version: 1.12.2
Forge Build: 2554
Mod Version: r1.4-120

To reproduce this effect; place a piston facing upwards, a solid block above that, a trapped chest on top of the block, and then open the chest. The trapped chest GUI opens for a split second, then the GUI closes; now open the chest again, then close the GUI; the chest remains in its open state and the GUI is inaccessible.

Of note is that moving the chest again with a piston will return it to its closed state.

I can reproduce the chest going up and locking the piston in place until it's opened again, but I can't keep the lid open and much less lock myself out of the GUI.