This bug has shown up in various forms over the course of development. This time it seems different in that it can occur either before or afer the dupe becomes incapacitated.
It's fairly unpredictable when exactly it will occur but it's bound to if you're sending your dupes into extreme environments with only a sweater for protection.
Ren, climb up. Ren. Ren!
Load this save and let cycle 731 play out a few times, it will eventually happen.