@OCMSP 

It's a symantics thing.  The controller is where all the config info resides, and when you move devices, they take on the config from the new controller, not whatever settings they appeared to have previously under the old controller.  However, with a little planning you should be able to split a site into two without having to redo everything.

To fix this, you basically clone the original controller (so restore a backup to a new controller instance) that will move all the original controller settings (WAN, LAN, VLAN etc.)  Then tweak the controller for it's new location (usually just changing the WAN parameters, controller name, maybe timezone...you get the gist).  It also moves all the devices over.  Now, it's a bit fuzzy for me as it was a while ago, but I think all the devices re-connected to the new controller ok.  If not, they will still need to reset, but at least the their configs should all be pre-built and get reloaded, so downtime should be but a few minutes each.

I think your use case is pretty niche as usually moving devices is a redeployment to a new site, not a splitting of an existing.