On Mac OS X, it's possible to configure the mouse and trackpad to invert the scrolling direction. This is referred to as "natural scrolling".

QDial and QSlider respond to mouse wheel events.

When you invert the scroll direction for the trackpad on a Mac, those widgets invert their scrolling direction.
However, when you invert the scroll direction for a mouse, the inversion isn't applied.

To reproduce:
1. Create and launch an app with a QDial or a QSlider.
2. Use connected (USB?) mouse to scroll up and down on the widget. Note which way the widget goes when you scroll down.
3. Open System Preferences > Mouse. Toggle "Scroll direction: Natural".
4. Try scrolling on your app again.

Expected:
Scrolling direction is inverted.

Observed:
Scrolling direction is unaffected.