Although this bug manifests in moc, it appears to be caused by QFile not recognising the volume label in a canonical file path returned by QFileInfo::canonicalFilePath()

Line 824 of preprocessor.cpp (moc) is:-

include = fi.canonicalFilePath().toLocal8Bit();

If this is changed to

include = fi.absoluteFilePath().toLocal8Bit();

the problem disappears.

I suspect there is a difference between the Volume label generated by 64 bit Windows to that generated on x86 versions and that QFile doesn't recognise the volume label for 64 bit versions.