<< ?And those females who commit lewdness together from among your women, then bring four witnesses over them from amongst you; if they bear witness, then you shall restrict them in the homes until death takes them, or God makes for them a way out. And those males who commit it together from amongst you, then you shall annoy them. If they repent and amend, then leave them alone. God is Redeemer, Merciful.? (4:15-16)
Firstly I would have to question if these verses actually refer to homosexuality (I have always wondered what they refer to). Secondly if they do (and even if they don't) why the difference in punishment between men and women?
I used to think that maybe this verse was referring to prostitution. This perhaps could explain the difference.