After setting up a UNC as a BBMD the other UNC's on that subnet are getting "network mismatch" errors in their standard output windows.
R2 UNC's with BACnet jar's earlier than 535a.
This type of error is indicative of a routing loop on the BACnet internetwork. UNC's with a BACnet jar prior to 535a when set up as a BBMD will broadcast on their own subnet as well as to the other BBMD's and this can cause that also.
Install BACnet jar 535a or later in the UNC that is the BBMD to see if this corrects this issue. If the issue persists investigate the BACnet internetwork for a router loop.