Controllers get their node address from eith an MBX module or a PC attached directly to the local mbus (via an mbi card).
If you have an MBX there is a node switch behind the front bezel of the module. All controllers on the same local mbus as the MBX will use the node address of the MBX.
But I suspect in your case it was from a PC that had it's mbi set to N12. Any PC on the local mbus has the potential to set the controller's node address, and the user has no real control over which PC does it. Best thing to do is to be sure ALL PC's that have an mbi card on the local mbus have their node addr set to the desired node addr of the controller. The setting on PC's can be found in the Control panel APACS applet.
Also note there is a node switch setting on the controller's transition board that must be set properly. The switch setting will inc/dec the base node setting of the controiller, depending on whether the base setting is even or odd.
Also if you have multiple PC's on a local mbus then it is recommended to assign all the same node, but space their RACK adresses out by two. Example" PC1=N0R1S11, PC2=N0R3S11, PC3 N0R5S11, etc. Technical Support can steer you to the manuals that cover the xtion bd setting, and they have a write up that explains the insight behind the rack spacing.
All that being said - it will take a reboot for your controller to obtain a new node address.