I think it all depends on the dynamics of the relationship between both parents. If the parents are wholly accepting of the other's partner, then I don't see a problem with it. After all, if the step parent loves the child then they would want what's best for that child, the child may even be more likely to approach the step parent if that distance (ie not blood related), makes them feel more comfortable and less embarrassed, and if the step parent is approachable and the same gender as the child, ie a girl is more likely to speak to a woman.