It's very common for the QAR to do that. From what I've seen it happens any time it repairs itself which will happen if anyone has attacked it before you get there and also if you let it get too far away from you as you attack it. My advice is never attack it unless it just appeared and stay as close as possible when you attack. Another issue is the ship glitch when you attempt to board, in my mind this might only happen to crews of 2 but I'm not sure. I recommend that if you decide to attack do so with a crew of more than 2 or try solo. Your ship will be locked in an infinite battle with a crewless QAR if that happens to you, the only way you get your ship back is to wait for the server to reset.