QComboBox on Mac - up and down arrows for scrolling items visible when not needed

The QComboBox exhibits this bug only on Mac when the following conditions occur:
1) So many items are added to the QComboBox that it has to add up and down arrows for scrolling its items.
2) The user clicks the QComboBox, so that its list with choices is displayed.
3) The number of items in the QComboBox is reduced to such amount that there is no need for up and down arrows to scroll the items of the QComboBox. There is no matter whether the QComboBox is:
a) cleared and then a small number of items are added
or
b) the number of items is reduced to a small one by removing items one by one (not clearing and then adding)

A Qt GUI project is attached to the bug report to depict and reproduce the bug.
Do the following steps:
1) Set the combo box to have 100 items.

2) The most important part: click the combo box, so that the combo box draws its up and down arrows. If you miss this step the bug won't be reproduced.
This step is not mentioned here: http://bugreports.qt.nokia.com/browse/QTBUG-18788

3) Set the combo box to have 10 items.
4) Again, click the combo box to reveal all of its items. Note that if you omit step 2) and click the combo box as late as now, the bug won't be reproduced.

Removing vertical and horizontal scrollbars of the QComboBox::view() - QAbstractItemView, and/or setting the number of visible items doesn't help.