Order of audio channels gets messed up in my timeline - help!

[torincdn]

I am working on some multichannel video in Premiere (I'm on CC version 14.5.0). Basically, I have a bunch of videos with 8 channel audio (8 discrete mono tracks) that I'm assembling into one big video playlist, it's a simple edit.

I've set up my 8 channels in the sequence correctly, set my track output channel assignments correctly, panned left and right, all as I've done many times in this setup. When I view my audio in the preview window, all is correct and it plays correctly. But as soon as I drag anything into the timeline, the channel order gets messed up and tracks play on the wrong channels. This is what I see for the audio waveforms in the preview window versus what happens when something is on my timeline.

Preview, all the channels as they should be:

Once I bring it into my timeline. My channel order becomes 1, 2, 3, 6, 7, 8, 4, 5:

This happens for any multichannel content I drag in, and the content is coming from multiple sources so it's not just stuff I've made. I can get around this by separating out my audio tracks from the video and reordering them one by one (ie. drag the track that's supposed to be in channel 8 from where Premiere is putting it in track 6 to track 8) but I have no clue why this is happening to begin with and it's driving me nuts.

Here's my track mixer and timeline, in case I've missed something:

Help?!

[torincdn]

Update - I'm able to fix this by going into Audio Channels and setting the checkboxes as they should be (track 4 being for channel 4 instead of channel 7, etc.) Still the most bizarre bug I've experienced in Premiere and I can't work out why it's happening.