Hrm, maybe my memory is off then. I recall it working in a version with the SI type interface, but maybe it really was OOTP 6.5 the last time this worked.
Either way, the design is kind of defies logic...I'm going to play you at SS, have you officially listed as a SS, and you're going to somehow improve your control and mastery of pitches just by by fielding ground balls and swinging a bit. It's the hot new training program for pitching prospects

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I guess it's not that important. I mean only the MLB roster set (Kelly, Blake Martin, Micah Owings) players have two-way potential, the game never really generates anyone who has enough potential to be a hitter and pitcher. So after you sim the first decade or so, there's no one you really want to convert anyway.
Maybe in a future version or big patch generated draft players can have two way potential. Any way I'll settle for the initially discussed bug/feature should being changed, as it just makes no sense.