CPU usage jumps to 100% when no UAV connected and remote TCP device disconnects

[dwaiting]

Steps to reproduce:

1. Start MAVProxy with UDP master and TCP out: mavproxy.py --master udpin:0.0.0.0:14550 --out tcpin:0.0.0.0:14550
2. QGroundControl connects to MAVProxy via tcpin link
3. Go to Comm Links in QGroundControl and hit "Disconnect" on the TCP connection

mavproxy.py CPU usage jumps to 100% and stays there:

    PID USER      PR  NI    VIRT    RES    SHR S  %CPU  %MEM     TIME+ COMMAND                                                                                                                                                                       
 822890 dwaiting  20   0  280876  77804  33712 S 100.0   7.8   2:08.59 mavproxy.py 

In addition to the problem with the CPU, MAVProxy will not accept another TCP connection at this point.

This problem occurs only when there is no active UAV connected to the udpin link. If there is an active UAV, QGroundControl can connect and disconnect repeatedly, and neither of the above problems are observed.