That's probably THE most common mod problem, and I still don't know what causes it or how to fix it. It happened to me the first time I modded the player window, but after that I haven't seen it crop up again in my own modding, but I hear people mention it a lot...
Can you attach the copy you've got? (Or Sunthas, can you attach yours?) I haven't actually taken a look at one with broken conc bubbles since before I actually knew what I was doing.
