I've got a form that is somehow getting undesired spacing when viewed in Mac style only: http://i.imgur.com/xoGNDZ6.png

Windows, GTK+ and Fusion styles are fine. Clicking on the little space on a Mac says it comes from a QHBoxLayout, however I've set all the values to zero: http://i.imgur.com/VhPGeVX.png

I'm having difficulty working out where is the undesired space coming from. It looks really jarring on the UI and I'd like to get rid of it as it is a visual quality issue. This is only happening when the checkable property is enabled on the QGroupBox.