No..its not a bug..Until you are plundered once, you can still be attacked again and again unless you lose or finish your convoy. You dont even have to be on the same part of the map. Once he lost the battle, he swapped his teams and went back to group base, where your SS would be still visible for him in plunder NPC. This is a natural thing, and my guess is his power is close to your supports. If his was less, then he would inform his groups some other higher powered plunderer who will attack. This is normal.. I know how it feels.

Edit: based on the newer replies the max time you can be attacked is capped at 3.

oh. well that *s. lol I was all like "yes! home free." then like 5 feet from safety, he got me. not a happy moment for me XD anyways, thanks for responding!

You can get plundered up to 3x max, so if people bounce against you 3x you will no longer appear in the plunder list. This is also why you normally dont get support that can be easily countered (eg: blitz), where if people test you, all they have to do is get some hard counter (hinata, han, etc) and beat you again. Of course....if you sync up with the person who is supporting you, you can try countering the counter if you want to be fancy :P

Yupz, just as Slacker~ said, a player on convoy can only be plundered 3 times in total. If the three attempts against the player fails, then the convoy will not be available to be plundered.

Lets say usually is not much smart to plunder the same person twice, because you are compelled to use the counter team also against the convoyer team and could be to match a team to beat the supporting one makes you actually lose against the convoyer one against whom maybe you won with your main team...

Alright, thanks everyone for the replies. :)