Xcode 3.2 not recompiling changed files

I've been programming a new iPhone application and everything has been chugging along fine, until this afternoon when I noticed that any changes I was making were not being reflected in the actual app! Even code that throws errors isn't getting picked up by the compiler.

To get around this, I have taken to the following procedure:

1. Finish making my edits, and add code to the file which will always throw a compiler error.
2. Right-click the file I have just edited, and hit "Compile" to just compile that one file; it will throw the error.
3. Remove the error-producing code, and again right-click and "Compile" the one file.
4. Build 开发者_高级运维the whole project

This is quite annoying, and I can't figure out why this would suddenly happen to my Xcode project. Any thoughts on what could be causing this, and how to fix it?

It appears that XCode thought (insofar as computers can "think") that my files were unchanged. "Touching" the files seemed to do the trick, sometimes, but not always.