I wanted to create a mono downmix of a stereo track. I tried using the Export Mono Downmix option of Export Audio Mixdown.
The mono audio track that resulted was way shorter in duration (2:22) than the original stereo audio track (10:29). But it was the whole track, compressed in time.
I tried time-stretching it to the original length, but it was full of artifacts and pitch-shifted 2 octaves higher than the original.
This seems like a bug to me, unless I am missing something.
The original track is in green and orange at the top. The downmix is in red below it.