is current master supposed to work with Mavlink 1.0 ?

What am I missing ?
Compiled and flashed two radios, (format changed, so all settings are default) radios connect to each other and appear to work fine (solid green LED, I see terminal traffic pass)
Once one is connected to a pixhawk (that emits MavLink 1), it starts blinking red , and both radio's green LEDs start flashing (connection lost)

No source file, test, or entry point is named. Start by reproducing the failure with a Pixhawk emitting MAVLink 1 and compare it with the radio-to-radio case; done means both radios remain connected and pass terminal traffic while attached to the Pixhawk.

Written by the indexing model from the issue text.