Nostalrius Begins - Quality wow vanilla realm (1.12)

Have had a problem with this since I made the character but when I cast skills, the castbar lags/jumps in the bar, its not flowing as it should.

Even without addons its still doing it, tried re-downloading wow so it would be fresh but still the same, anyone had this problem? Also not MS problem.

Short clip on what I mean, look at the bar.
http://im.ezgif.com/tmp/f5f27cc118.mp4

I have also same issue. Did you find a solution for that??

Have same problem. Any chance to fix it? Really annoying.