QMdiArea's QScrollBars does not recalculate while ScrollBaralwaysoff

here is the bugs steps:
1、add a QSubwindow to the QMdiArea, and make sure the QSubWindow in the normal state(QMdiSubWindow->showNormal(); )
2、resize the subwindow to make sure that the scrollbar of mdiarea could be saw.(subwindow->resize(mdiarea->width()* 2, mdiarea->height() * 2); )
3、Set the QMdiArea's Scrollbarpolicy to Qt::ScrollbarAlwaysOff.
4、resize the subwindow's size.(subwindow->resize(width() / 3, height() /3));
5、found that the mdiarea' scrollbar still could be operated by mouse wheel, and the scrollbar's max value didn't not be recalcuated (qDebug() << mdiarea->VerticalScrollBar()->maximum; )

General speaking, the scollbar should be recalcuated even if the the attribute ScrollbarAlwaysOff has been set, for that the "ScrollBarAlwaysOff" just mean that the scrollbar could not be saw but not disable.

here is the bug attachments: