I started to play Engineer's Life, which includes the portable crafting table in it as an addon. Problem is, there seems to be no check for if you have it open when you attempt to click and move it. I have caused a crash (with either made the game go unstable, or flat out crashed it) several times by accidentally taking the newly crafted item, or something else, and trying to drop it into the same hot bar position as the crafting table. A lot of other mods, which do something similar, seem to have something in them that goes, "Heh, Someone clicked me, and this should pick me up. But they can't do that, because my GUI is open.", and ignore the attempt. The PCT is quite happy to let you pick it up, while you are in the middle of using it, and.. apparently this causes the client/server to lose track of... may what the GUI belongs to, or something? But, it either generates an error, telling you to hit ctrl-I to figure out what it going on, or flat out crashes the game.

So, simple way to replicate it, at last in the version in Engineer's Life - craft any item, then, leaving the GUI for crafting "open", attempt to replace the crafting table with the newly crafted item, in the same hotbar slot. The game will "pick up" the PCT, and, depending on how massively it blows up, either generate an error, or crash the local server (I assume it would also crash a remote one).