print_progress_dialog.h is only included once, so the include guard protection never comes into effect. If you unnecessarily include it e.g. in core/map_printer.h the compilation fails.
print_tool.h is also included only once. Here the failure occurs if QT_PRINTSUPPORT_LIB is not defined. However, in print_tool.cppprint_tool.h is not included if QT_PRINTSUPPORT_LIB is not defined, so the error is masked and never comes into effect.
These bugs didn't lead to a compile error since
print_progress_dialog.his only included once, so the include guard protection never comes into effect. If you unnecessarily include it e.g. incore/map_printer.hthe compilation fails.print_tool.his also included only once. Here the failure occurs ifQT_PRINTSUPPORT_LIBis not defined. However, inprint_tool.cppprint_tool.his not included ifQT_PRINTSUPPORT_LIBis not defined, so the error is masked and never comes into effect.