DEPENDPATH causes source files to be found

In src/tools/bootstrap/bootstrap.pro there are incorrect paths in SOURCES for the zlib. But this is not the concern of this issue. Our concern is why this does not fail. Qmake manages to find these files and creates makefiles with correct paths.

Using qmake -d 255, it was discovered that the files are found using VPATH. We suspect that DEPENDPATH is responsible for this. If so, this is at odds with the description of DEPENDPATH in the qmake documentation where it is said to be about include files.