Outpost opponent "bonus attack" - wth?

Outpost assault opponents sometime have a "bonus attack" against you. Sometimes when you get close. Maybe others, e.g. Hunters. I can't find that it's a weapons, jacket or survivor trait. What's up with that? Thanks.
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There's also the Retaliate Trait. Daryl has it and he's placed in a bunch of outposts for that reason. It's also common with the melee survivors. If you hit them, they can hit back if the trait kicks in.
Here's a good explanation: http://forums.nextgames.com/walkingdead/discussion/16434/interrupt-overwatch-issue-with-freemen-bonus-attack
Thanks for the link!