bluetooth rfcomm# does not show up as port for Serial Monitor in linux

Ubuntu Linux 14.04.2
bluetooth rfcomm# does not show up as port for Serial Monitor in arduino 1.8.1

It does not up under Tools->Port. Only /dev/ttyACM0 shows up.

It's not just a refresh problem, as connecting /dev/rfcomm0 prior to launching arduino 1.8.1.
It does show up as a default board listed on the bottom right such as:
Arduino Yun on /dev/rfcomm0

It won't show up as an available serial port if I connect rfcomm0 after launching arduino 1.8.1

/dev/rfcomm0 still shows in the bottom right of arduino even if I delete /dev/rfcomm0 before launching arduino.

I am using teensy 3.2 device, but even before installing teensyduino, this is the behavior.

Start by reproducing the issue in Arduino IDE 1.8.1 on Ubuntu 14.04 with /dev/rfcomm0 connected before and after launch, then inspect the Tools → Port entry point. Done means /dev/rfcomm0 is correctly listed as an available serial port and its listing updates when the device is connected or removed.

Written by the indexing model from the issue text.