15B7 Loosing audio sync point when changing channel

I am testing out Resolve 15 Beta 7 on Mac OSX Sierra, and imported a current project from 14.3 and noticed one clip audio had lost sync. I have narrowed this down so that it is repeatable in a new project.

I have an MXF video file with 8 embedded channels (only two in use) and a separately recorded audio file with 6 channels.

Below is the process I have followed to setup the media and link the audio, and the issue that arrises. I want to always use the separate recorded audio.

1. Take Video Clip and line up clapper board in the media pane source window.
2. Click on related audio file and line up for the clapper sound, then click the link button.

All is synced. Now I go to the clip attributes of the video file to remove all channels bar 1 mono and map this to Linked clip Track 3. I do this to make the rough cut edit timeline simple and easy, as I will deal with audio later in Fairlight etc. by duplicating required audio tracks and assigning the desired channel.

If I then drag the clip to the timeline, all plays as expected. If I then click on clip attributes of the clip in the timeline, and change the audio track from Linked 3 to Linked 5 and return to the timeline, the audio sync point seems to have been reset and the playback starts from the beginning of the original audio file not where the clapper board was set. If I change it back to linked 3, it's fine.

So it seems to not maintain the sync point.

If I change the clip in the same way in the media pool, the media pool clip plays correctly, but when dragged into the timeline it reverts back to the beginning of the audio file.

EDIT
I have randomly tried other clips and followed the same process and they too exhibit the same issue.