That doesn't make sense. Otherwise why would the wilds have Gender? I have the amigo version that shows illustrated figures of exchanging jokers. Male fo male. Female for female. BSW has some known bugs on this game. I have seen alot of them in my 300 gameplays on there!
I'm curious what known bugs there are on BSW. I play CI for the my town in the StadtLiga, so "inquiring minds want to know" .
Giving wild cards a gender limits their flexibility and power. Allowing any legal card to replace and claim them (rather than just same gender) in a sense limits their power as well because your opponent will be able to immediatley claim a wild you just played in more instances.
For what it's worth, I believe the english translation I read says the joker can be replaced "by a corresponding card" or something like that. I'll try to ask one of my german speaking friends to help with the german rules (and possibly scan the forums at BSW).
The English "Mattel" rules state: "...joker....may be exchanged for a customer of the appropriate nationality provided that the seating arrangements are still legal." The latter part of this rule leads me to believe that gender doesn't matter. If one had to swap with same gender, one wouldn't have to worry about the seating arrangements being legal still.