Sometimes AI doesn't react to sounds and fire. I'm not sure about the reproducibility, but it happened to me several times.
Video:
1-http://youtu.be/kRNUXMxM8nQ (took in the single player "Adapt" campaign, during a scout mission. It was the the secondary objective called "Elite Warriors" and I had to kill the special forces inside Syrta city).
2-http://youtu.be/M37nMqDeJjI (took in the editor, but I don't know how I got this happening: other times, when I tried reproducing the same situation, the bug didn't appear)
3-http://youtu.be/ABmPE5_2iTg?t=6m25s (single player scouting mission, objective "One shot one kill")
UPDATE: I've attached both a mission I've made where you can see the bug, and the .rpt file after playing that mission. {F25474} {F25475}