Wiring a Breaker Box

I'm setting up a small system and have a couple of questions I'm hoping someone can help me out with.  I'll be setting up 2 Sharp 80W panels to start with an outback MX60 charge controller, an MK105Ah battery, and a Midnite MNPV3 breaker box.  I'm looking at the schematic from the Outback MX60 and am confused as it is showing a shunt between the negative of the battery bank and the negative terminal of the inverter.  In the schematic, the shut appears to be tied to the terminal bus bar, but it is not clear how.  The ground bus bar also appears to be tied to the DC negative bus bar.  Does this make sense?  I'm new to solar, so thank you to anyone that can help.

Steve