Okay that's helpful! I just tried replicating it, but wanted to check a couple things with you to help me nail it down:
1. Were you in fullscreen? Using multiple monitors/displays?
2. Were the controls set to default?
3. Which browser/OS was it? Any special language settings?
4. Were you near a downed enemy (with prompt for nonlethal takedown)?
5. Did you have an offhand equipped or click left or right mouse button when it happened?
Thanks!