It has to be a retail bug. According to WoWHead, Binding Shot lasts for 11s (10s on PandaWoW), so if you got stunned (in PvP) by it, you would have to wait 3s until cc effect ends (it wouldn't work even if you broke cc effect because there wouldn't be enough time to give Binding Shot an opportunity to restun). Therefore, Binding Shot shouldn't be able to restun you because you would be inmune for 10s to its effect (as you already got stunned) and there would be just 8s or less (7s or less on PandaWoW) left until Binding Shot effect ended.
Changelog: http://prntscr.com/qvwrow