Treasure Bandit Glitch

I saw a Treasure bandit and started to hit it with Magic Missile with my wizard, after a few hits I wasn't able to target it any longer. Also the Treasure Bandit jumped into his portal and it was gone, then a second later the portal opens again with his soundbit jumping it again and again...

I also ran off screen and came back to see the Treasure Bandit respawn but I was still unable to target him again. He did start to drop gold again, but the situation ended up being the same, he just spawns the portal in a different location and it keeps on repeating.

I encountered the same problem during the same playthrough at the Royal Crypts area. I again shot at the Treasure Bandit with Magic Missle to the same effect mentioned above.

Here is a link to the video I captured:

http://www.youtube.com/watch?v=vJvZMVsnHKo

I'm running Windows 7 Ultimate 64bit
AMD 1090T 3.2Ghz
ATI HD 5770
16GB RAM