I normally use Single AF, and haven't (consciently) tested it in other modes. I'll do that tomorrow, when it's daytime. I had already remembered of cleaning the contacts, but they look quite clean, so I left them as they where. Maybe it needs a software upgrade, like Satinsnow suggested. I'll have to contact Minolta here.
About quality, I like it a lot. Little distortion (very little), minimum flare, good optical quality, good build (although the built-in hood handling is a little fragile). It is great for street shooting, as I can get the people without being on their nose. Only real downside is the AF speed, quite slow, but it doesn´t bother me much.