@Fern: For the scenario you mentioned (he said, she said) this law makes zero difference. One of them is lying and the police will have to prove the rape. If proven, a party will be guilty of rape + perjury or the other party will be guilty of perjury + obstruction of justice.
This law, if I understand its intention correctly, applies to situations where a victim is unable to give consent (obviously) or you are unsure if your partner is attracted to you. Acquiring consent will effectively give you an immunity. If your partner is willing to lie to the school/police/court, she or he should be punished accordingly. In that sense, this puts additional burden on the accuser if she or he gave consent because it will be more difficult to claim the consent was not genuine or some such.
Again, whether this is a wise law or this law can even be enforced - I do not know. I have not given much thought about it. Nevertheless there is no switch of presumption as far as I can tell here.