Wrote this to report the bug, might as well womplement this thread instead of flooding with a new one :
The "Mobile" perk doesn't work like it's written when I chose it
According to the perk, my character should be able to not suffer AoO when exiting the range of the target he attacked in melee,
as it applies the "mobile foe" condition to the enemy and(???) the character who benefits from the perk, seeing that, I did just walk away and this was the result :
Good luck with that, computer wizards, sorry to bring bad news on this one.