We have performed a kinematically complete experiment on ionization of H2 by 75 keV proton impact for electrons ejected with a speed close to the projectile speed. The fully differential data are compared to a three-body distorted wave and a continuum distorted wave - eikonal initial state calculation. Large discrepancies between experiment and theory, as well as between both calculations, are found. These probably arise from a strong coupling between the ionization and capture channels, which is not accounted for by theory.