title: Xcode 4 doesn't rebuild headers despite "Scan all source file for includes" being on
body: <p>Pretty much what the title says. I have the build option ticked, but changes to my header files aren't noted unless I clean and rebuild.</p>
  
  <p>So, for example, when I add a member to a class in a header file, and try to access that member from some other source file, Xcode/compiler will tell me that member doesn't exist. When I clean and rebuild, the error is gone and everything works as expected.</p>
  
  <p>It doesn't happen on a fresh project, so I'll try and reproduce it.</p>
  
  <p>Anyone know how to fix this? </p>
  
  <p>Cheers,</p>