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?

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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.