[OS X] Wrong font used for displaying inactive QTabWidget and QTabBar elements

Qt 4.8 had an issue that persists in Qt 5.5.1, in which the native widget used to display tabbed interfaces (QTabBar and QTabWidget) uses the default system font for inactive (unselected) elements instead of the font configured for displaying the widget. The selected element is shown with that font, and the width of all elements is calculated using that font too, which can lead to truncation or multi-line display of text in the inactive elements.
The 1st attachment illustrates this issue in a modified version of the tabdialog example.

Switching the widget to documentMode does not "fix" the issue once it is up and running: see the 2nd attachment.
However, switching it to documentMode as the 1st thing after creating it does fix the issue: see the 3rd attachment.
Note however that the widget will then use a smaller font; I have not yet been able to confirm if this is expected/correct or not.

This issue does not occur when using a different QPlatformTheme or QStyle (e.g. with -style fusion).

Edit 1:
Apologies, I was expecting attachments to show up in the order of uploading them
1st: tabdialogMod-native-altfonts.png
2nd: tabdialogMod-native-altfonts-switched2DocMod.png
3rd: tabdialogMod-native-altfonts-startedDocMode.png

Edit 2:
I have scanned through the QtBase code, expecting to find instances of NSTabView or NSTabViewItem. I have been unable to identify the underlying implementation however.

Edit 3:
I no longer notice this issue with Qt 5.6.1