Clip panning plays correctly but isn't rendered on bounce or mix down

I've reported this bug on the UserVoice forum but I'm just going to put it here as well in case anyone else is wasting time struggling with it!

I'm using Audition 14.2.0.34 on Intel Mac

When a stereo clip is on a stereo track the clip pan envelope sets the balance between the left and right channels. If the clip pan is set to L100 then you will only hear the clip's left channel. If that stereo clip is a 2 channel clip created from 2 channels of a multichannel audio file then the pan envelope will work correctly on playback but will be ignored on mixdown.

To reproduce the bug:

Create a new stereo multitrack session
Open a multichannel audio file, select two channels of that file and drag them onto a stereo track. (Depending on your settings Audition may try to put the two channels onto two different tracks, in which case hold down option as you drag)
You should now have what looks like a stereo clip.
Make sure "View>Show Clip Pan Envelopes" is selected
Drag the Pan Envelope up or down to L100
When you play the session you'll only hear audio from the left channel
Right-click on the track containing your panned clip and choose Bounce To New Track>Selected Track
The audio on the new track will contain audio on both the left and right channels
Choose File>Export>Multitrack Mixdown>Entire Session
The exported mixdown will contain audio on both the left and right channels.

Workarounds are:

Once you've dragged the clip to the Multitrack Session, choose Clip>Convert to Unique Copy. This discards the unused channels and creates a new stereo source file. The problem with this is that if you've already got panning envelopes in place they are lost when you do this.

If you have a long clip with complex pan envelopes already in place which you want to keep, click on the clip to select it, position the playhead just before the end of the clip, choose Clip>Split, drag with the cursor to select the main clip and the small slice at the end, choose Clip>Merge Clips. This effectively bounces the clip in place, correctly applying any envelopes.