GPIO - problem defining input and output pin on the same gpio connector...

Hello everyones!

I know this is a fairly basic question but this puzzel me a lot... I have tried to do a simple loopback on two pins (A0 and A1 on the same GPIO connector on a DE2 kit) defining one as input and the other as output and shorting both pins together but (I know...it is too simple to work!!) Quartus is telling me I cant do that. By defining both pins as inout it work...

Anyones care to explain why? I dont want to stay in that puzzel state the rest of my life!