GCS Link Quality indicator incorrect with MavProxy redundant connection

Using MavProxy, I have two links to the same Pixhawk (APM plane 3.7.1):
Link 0: USB-->SOCAT (on OpenWRT)-->UDP port 14506 over WiFi Mesh -->MavProxy
Link 1: 3dr 915Mhz radio --> MavProxy

Mavproxy command is:
mavproxy.py --master=udpin:0.0.0.0:14506 --master=/dev/ttyUSB0 --out=udpbcast:192.168.10.255:14550

Mission Planner (1.3.43) connects using UDP to 14550, and that works fine. These connections work very well individually, the link quality indicator in MP reads accurately. However, when I use it as above, in a redundant configuration, the link quality indicator reads 3% (though it's clear by observing the status tab that the mavlink stream is coming through just fine). It also fails over and re-establishes just fine when either connection is lost.

My guess is that something in the mavlink sequence is different between the merged USB and 3DR connections, causing MP to misjudge the link quality. There is also a possibility the issue is with MavProxy.

Start by reproducing the reported setup with Mission Planner 1.3.43, MavProxy, the two masters, and UDP port 14550. Compare the link-quality indicator with the status tab while each connection is used alone and together; done means redundant connections report accurate quality without breaking failover or reconnection.

Written by the indexing model from the issue text.