QFileSystemModel.isDir() returns wrong value

When using QFileSystemModel the isDir function returns false even if the file is a directory. This happens when the QModelIndex object is returned programmatically using the model.index(QString &path) function on a path that was not accessed via the GUI viewer object.

Example (see attached file):
index = model.index("C:\\Qt\\4.8.3\\include
QtGui");
model.isDir(index); // Should be True, returns False