When a QComboBox within a QDialog with a Qt::Sheet attribute is clicked, the QDialog's window decoration shows.

I have a QComboBox inside a QDialog which has the Qt::Sheet window flag. Therefore, it should, on OSX display as a sheet. This happens as expected, however when the QComboBox is clicked, the QDialog's title bar appears which allows the user to move the QDialog around (unwanted/unexpected behaviour).

Code to reproduce this issue and screenshots are attached.
I also made a thread about this issue on the Qt Forums: http://qt-project.org/forums/viewthread/31622/