why mission planner can not connect with internal bluetooth port directly!Thanks

My APM communicate with GCS（MISSION PLANNER）by XBEE,The ground xbee connect with a bluetooth model,and I want MISSION PLANNER connect the bluetooth model by computer bluetooth port directly,and failture,only use the software "Serial to ethernet connector" convert bluetooth port to TCP server,and MISSION PLANNER connect the TCP server,then connect with APM successful! I want mission planner can connect with bluetooth port directly!Thanks
project1:APM<--->xbee<------------------>GCS xbee<--->bluetooth model<------------>computer internal bluetooth port<-------->MISSION PLANNER:failture!
project2:APM<--->xbee<------------------>GCS xbee<--->bluetooth model<------------>computer internal bluetooth port<-------->software "serial to ethernet connector"<------->MISSION PLANNER:successful!
project3:APM<--->xbee<------------------>GCS xbee<--->bluetooth model<------------>external bluetooth serial model <------->MISSION PLANNER:successful!

The issue does not identify a source file, test, or entry point. Begin by locating Mission Planner's connection handling for computer Bluetooth or serial ports, reproduce the direct Bluetooth failure described, and consider the work complete when Mission Planner connects directly without the Serial to Ethernet Connector workaround.

Written by the indexing model from the issue text.