How to export mix to a stereo file? (Panning position is ignored) Solved: Track Automation

I am trying to export my mix to a Wave file but whatever I do, I just get a mono mix.
 
I have a trivial project with two audio tracks of identical length and one master bus.
 
I pan the two audio tracks hard left and right. If I play back, I hear stereo.
 
Now I want to export this, so I click Files->Export->Audio, select Category Buses/Master (I also tried Entire Mix and Hardware Outputs), I set Channel Format to Stereo and I export.
 
The result is physically a stereo file, but both channels are an identical mono mix.
 
If I play my project, it's stereo. The VU meter and Waveform Preview in the master bus confirm its stereo.
 
If I turn off Fast Bounce and watch the export as it happens, the master bus VU meter (and waveform preview) clearly show both channels are moving identically. Both channels are a mono mix.
 
What am I doing wrong?
 
More details: Exporting to Wave file, 44k1/16bit, triangle dithering, all the check box selections are off (except Fast Bounce)
 
The audio tracks are freshly recorded from a pair of microphones with no effects and nothing in the Pro Channel. They are definitely panned hard left and right.
 
For fun I tried Split Mono. I got two identical mono files, both being a mix of both channels.