there are differences in how bluetooth drivers assign com ports.
on one system, ports are assigned on the fly, and don't proliferate when you swap devices. on another system, pairing up the new devices creates fixed assignements for the ports that each device might use, even on each physical input port.
there are some trade offs here, generally this creates a ton of com port assignments on a system -- the more devices the higher the assignments. that alone can become a hassle. you may have to manually re-assign those ports to lower numbers to get software to work too, or keep re-assigning ports when you swap out devices.
a lot of software out there isn't too smart about extended, or higher number ports. though, i do like the simplicity of serial data.