Text is aligned to top in comboboxes (see the attached screenshot). There is a Qt issue for this behavior: https://bugreports.qt-project.org/browse/QTBUG-32789.
A possible solution: http://successfulsoftware.net/2013/10/23/fixing-qt-4-for-mac-os-x-10-9-mavericks/
Another solution: update Qt libraries to version 4.8.6.