I went to research a new plane, and saved up lots of free experience to upgrade the plane completely. A day later, I notice the previous aircraft still has all it's experience points, and my free exp is basically wiped out. On top of that, the previous aircraft is completely upgraded, there is no second optional aircraft to research, and I can't even turn its experience into free experience. If we were talking 10 or 20k I'd live with it, but we're talking about 94k. So, I probably screwed up, but what did I do wrong? I've never had this problem before.