Chris: While turntable control is no longer a problem you are concerned with, for others following this conversation, it may be useful to know that the details of turntable control are embedded in the turntable's DCC decoder and not in JMRI.
From what you describe, you may have a Walthers (ie Heljan) turntable. I have and it's DCC decoder is such that each end of the moveable track has a separate DCC address (far end = near end + 1).
The spurs on the opposite side of the turntable from the engine shed tracks prevent a runaway loco derailing but are not necessary for operation. I don't have them and a runaway comes to an abrupt stop when it derails harmlessly.
Jan
