Qml Loader progress does not update correctly

The Loader item has a progrss which claims to be between 0.0 and 1.0. When loading files which have a visible delay in appearing on screen, the progress changes only once (directly to 1.0),

The below loader:

Loader

With a variety of local and non-local files never printed any value x, such that 0.0 < x < 1.0 .