QProgressBar using Qt::WA_MacSmallSize is vertically mis-aligned

Attached is an app that displays three QProgressBars, from left to right, with the Normal/Small/Mini Mac size attributes turned on. Each QProgressBar is vertically aligned within the window, and over a red centre line.

The Qt::WA_MacNormalSize and Qt::WA_MacMiniSize progress bars line up correctly with the centre line, however the Qt::WA_MacSmallSize progress bar is displaced vertically upwards.