As you can see, all the mass fractions on the inlet are constant (figures shown for h2o and o2, hence n2 is also constant). All mole fractions should therefore also be constant. However, the figure shows there's a 10% change in mole fraction on the boundary. 

Convergence for that case was good (steady-state). Also, I think convergence shouldn't play a role here? As mole fraction is a post-processing variable (mass fractions are use in the transport equations), and the mass fractions on the inlet boundary are fixed. 

Mass fractions of h2o and o2: 

Mole fractions of h2o and o2: