I tested with Hopper, Extra Utilities 2 Transfer Pipe and Thermal Expansion Item Duct, they all causes the crash when place on the side or on top of the crucible while feeding into it. when inserting Empty Bucket and Lava Bucket it seem to crash, this probably include any item that grab liquid. Haven't got time to test those yet.
EnderIO instantaneous pipe with Extract and Insert seem to not crash the game tho.

To reproduce:
Step 1: Place a Fired Crucible and a Hopper next to it or on top of it, make sure the Hopper is facing the Crucible so it would insert item into it.
Step 2: Place or drop bucket into/onto the Hopper.
Alternative Step 1a: Use Transfer Pipe and Chest, setup it so that it would pull item from the chest and into the crucible.
Alternative Step 2a: Place bucket into the chest.
Alternative Step 1b: Use Itemduct with Servo and Chest, setup it so that it would pull item from the chest and into the crucible.
Alternative Step 2b: Place bucket into the chest.

Final Step: Watch it crash and burn.

crash-2018-01-13_10.26.10-server.txt