Not a bug per se, as the program is behaving as designed. But isn't the database a little strange? I mean, it's a frequent case of tricky unbalance. I'm not sure such unbalances add a lot to the game. I'm not sure they are realistic either(maybe they are, but I'd like to be pointed to sources).
But the interface is clearly misleading there. For whoever does not read the forum, it's nigh-on impossible to guess that. The message should at least say "on return leg", "on both legs", or something like that.