The following code produces an invalid preprocessing expansion under Creator:

#if !defined(X) && defined(A)
foo
#endif

#if defined(A)
bar
#endif

If you paste this in Creator, you'll see that the "bar" line is greyed out because A isn't defined, but the "foo" line has a white background. Somehow, Creator thinks that the condition evaluated to true.

Placing parentheses around the negative (as "(!defined(X))") does not help.