Multichannel audio: Tracks not shown in audio clip mixer

In fast turnaround edits I usually string out all clips from the camera card into a sequence, load it into the source monitor and edit from there. This gives me a fast way to scrub through all the footage from the card. Because the clips have multchannel audio, I usually only want to listen to a specific track. e.g. boom mic, lav mic, camera mic etc. To do this, I can solo or mute tracks in the audio clip mixer. In version 14.3.0.25 this doesn't work.

Steps to reproduce bug:

1. Import clips with multichannel audio. e.g. XDCAM HD422

2. Create new sequence from imported clips.

3. Load sequence in source monitor.

4. Check audio clip mixer to solo/mute tracks.

 
Result:

Audio clip mixer only shows one track. Seems like only the first.

Expected:

Audio clip mixer should show all available tracks to be able to solo/mute. e.g. XDCAM 8 tracks

Premiere version 13.1.5, behaves as expected.

System info:

Premiere Pro (Beta) v14.3.0.25

MacBook Pro (15-inch, 2016) 13,3
macOS 10.14.6 (18G4032)
2.9 GHz 4-Core Intel Core i7
16 GB 2133 MHz LPDDR3
Radeon Pro 460 4 GB

OWC Thunderbay4 Softraid RAID5