Logic Pro X Weird mix down bug in one song.


I'm doing my normal "flatten and merge" thing using track folders today and for some reason Logic is asking me to mix the file down in mono or stereo instead of just flattening it. The same thing is happening when I go to join audio files together or use the glue tool. Weird. It's fine in a new blank project or if I import one of the odd tracks into a blank project. Any ideas?