Was messing around with the tunnel bore, it was active, digging a wall. Placed a chest card behind it, shift right click chest cart with crowbar, then right clicked the tunnel bore and it crashed.
Crashes on loading the world now too.

crash-report: http://pastebin.com/sECxdrum

It's like an easter egg hunt but with bugs \o/

Right... that would appear to be the newly written and completely untested capability inventory code that I wrote a couple months back when nothing compiled.

So much untested code. T_T