Had this happen in an Advent HQ raid the other night -- flamethrower ambush on an 8-man rainbow pod with a Gunner Kill Zone set up resulted in no shots by the gunner. The technical had the Napalm-X skill, which panics can panic enemies.
Apparently this is a (known?) issue where panicking the group leader affects the order of concealment/revealment and results in no overwatch shots.
Some folks thought it was fixed, but I'm experiencing the issue in 1.4. Discussion here: http://www.pavonisinteractive.com/phpBB ... 15&t=26269
No mods affecting gameplay other than cosmetic or QOL.