A comparison of full kinetic and hybrid simulations for Te/Ti>1, where Te(Ti) is the electron (ion) temperature, indicates that contact discontinuities cannot persist in collisionless plasmas. A simple analysis suggests that the potential barrier to ion mass and thermal transport identified by Wu et al. [1994> in their hybrid calculations can preserve the contact discontinuity if the contributions of electron thermal transport are small. When Te/Ti>1, electron energy transport in kinetic calculations results in large potentials which reduce the effectiveness of the potential barrier. Thus, contact discontinuities are unlikely to be observed in spacecraft observations.