We identify two possible paths for the progenitor evolution of observed WNE+O binaries with WNE/O mass ratios close to 0.5 and periods between 7 and 10 d. We show, through detailed binary evolution models, that with the assumption that the O-type star expels most of the matter flowing at it during mass transfer, one possibility to obtain the observed systems is through Case A mass transfer. We find a second solution using standard common envelope evolution. We conclude that in either case the O-type star in the three investigated systems did not accrete significant amounts of mass. We discuss the intricate situation that in other cases massive close binaries may evolve conservatively.