Make sure your camera is in AF.A or AF.S before you switch it to your MF lens. It's one of those lame
firmware bugs they still haven't fixed. And yeah, it doesn't work with autofocus lenses (even my Tamron 70-200mm which has an AF/MF switch on the lens). That's also on the wishlist...
If your AF mode is set correctly before you attach your 50mm, then it should work. The body AF/MF switch also needs to be on AF. Does it just take pictures even when you set it on the wrong focus?
It should work with all K/M/A series lenses, and if your tubes short out the contacts on the lens mount (or you do manually with foil. Workaround is on the wishlist, of course), it should also work with them. You can also play with reversal rings and stick that 50mm backwards on to your DA 18-55mm.