Yes, I had one hot (red going out) and another hot (black going out), and neutral (white) tied to what I thought was U5+6. With it attached to my little subpanel box, each leg was hot, but I couldn't get 240v out of it, because, as you say, each leg canceled out the other.
For now, I only have one circuit with 240v, the plug for my arc welder. The other 120v circuit always worked fine. Only when I tried to use the 240v would they cancel each other out and the arc welder would never work.
I think, (based on my faulty memory) that the original doghouse was connected correctly, only the (one or more??) leads coming out of the windings were labeled incorrectly. Had I not replaced the doghouse, everything would have worked fine and I would never have known about the mislabeling. Oh well.
Ray
PS - after re-reading my first post, I think what I meant to say was I was getting 120v from either U1 or U2 to neutral. When I measured across U1 to U2, I got almost nothing.