I see the same problem, it seems to be caused by the webGl linear sampling.
For now, you can solve that by switching to Point sampling in the project properties.
I wonder if it's a graphic card issue as Cross_ doesn't seem to have this problem.
If it helps, my card is a NVidia GTX 460 and I'm on win server 2008 r2 (it's like win 7) 64bits.