QMake silently skips source files it suspects of circular dependencies

Create the following two files:

Source.c:
#if !defined(AAA)
#include "Include.h"
#else
// Code here
#endif

Include.h:
#define AAA
#include "Source.c"
#undef AAA

Now, include Source.c into the SOURCES line of the QMake project file (.pro) and run QMake. The resulting Makefile will not contain any mention of Source.c and no error messages will be printed when generating it. A close analysis of the above example shows that these two files DO NOT constitute a circular dependency, but QMake apparently sill thinks that they are.