Reporting against 2.4.3 but probably applies to all releases.

When trying to build my project after adding QWinWidget, I got a nastygram out of moc which was the result of directory names in the include path that contained spaces:

10>moc qwinwidget.h
10> moc: Too many input files specified: 'D:\Users\amonra\Documents\GitHub\DSS\DeepSkyStacker\qwinwidget.h' 'Files' '(x86)\Visual' 'Leak' 'Detector\include'

My VS2017 C++ Additional Include directories was set to:

.\GeneratedFiles$(ConfigurationName);.\GeneratedFiles;"C:\Program Files (x86)\Visual Leak Detector\include";.;../Libraw;..\ZClass;..\tools;..\LibTIFF;..\CFitsIO;..\Zlib;%(AdditionalIncludeDirectories)

and the moc settings in VS project properties are set like this:

It worked OK when I removed the quotes around

"C:\Program Files (x86)\Visual Leak Detector\include"

So that does rather confirm the problem.

PS Yes, I do know VLD is less useful with Qt than it could be because of all the global objects Qt creates but ...