Numerical diffusion in ccm and fluent
 

So I recently worked on a laminar mixing species transport problem in Star. I had done this problem in Fluent before and gotten good results, so I wanted to see how robust star's solver would be. It was a simply Y connection with two similar species. I noticed that, unless I had the mesh aligned with the flow, I got crazy amounts of numerical diffusion. The same problem in Fluent however was handled (similar mesh size and settings, also unstructured) just fine, with almost no noticeable numerical diffusion.

I have three questions:
1. Has anyone experienced this before?
2. Is this a sign that Star's solver might simply be weaker?
3. Does this mean that their solvers for all other equations might fall to the same weakness? I.e. should I be worried about momentum and turbulence models being too diffuse?