Complex sentence: In the past, game designers have sometimes failed to think through all the implications of their rules, thereby leaving some details to be ruled on later or even post-mortem, such as the details concerning en passant in Parton's Alice Chess.
Split into simpler sentences: In the past, some game designers have failed to think through all the implications of their rules, thereby leaving some details to be ruled on later or even post-mortem. An example is the details concerning en passant in Parton's Alice Chess.