So, I take a shot at the fugitive, and everyone of them attacks me, pirates and hunters alike!
As I have been tracking those (and others) attacks inconsistent with the in-universe story, I have quite a few traces telling me what is happening on the piorityAI when the player is involved, so I was able to track this one down: the fugitive I attacked sent a message to its group peers asking for help when I hit it, and, surprise, the hunters where part of the group!
There were not two groups, one pirate group and one hunter group, there was just a hunter group, and the fugitive was part of it...
It boils down to ships defined in shipdata.plist with bounty > 0 and both hunter and pirate roles... when a hunter group is spawned, if that ship is chosen to be part of it in the random process, its group peers, having a bounty-hunter AI, will attack it, since it has a bounty, leading to free-for-all melle when the help requesting messages start flying around... _very_ story-inconsitent, and a trap for the näive player when he comes around

So, if you are creating a ship in you OXP, please don't mix hunter and pirate roles in the same datakey if you are defining explicitly a bounty for the ship!