Elevtions seem really prone to just make lots of mistakes. When they get confused, they just leave things out. It seems like they don't handle overlapping or intersecting objects too well, but I have never really figured out the secret. You can be working on an elevation or section and all of a sudden the thing just breaks and half of the lines will be missing.
If you remove the curtain and elevate it all by itself, do you still have problems?
Would you post the file so we could take a look at?