We sometimes create new build configurations that have a #define set by specifying the following in the qmake 'Additional arguments' box:

"DEFINES+=SOME_DEFINITION"

However, when using one of these configurations code like the following will be treated as if SOME_DEFINITION is NOT set:

#ifdef SOME_DEFINITION
// Some code
// This will be displayed as if SOME_DEFINITION isn't set
#endif

This also means that intellisense, etc. will not work in code blocks like this. The code compiles correctly - this seems to be an issue with the editor.