BT: [REG] Windows: painting issues when a modal dialog, which has a dialog as its parent which is parented to another window, is shown

On Windows, when a modal dialog is shown which has a dialog as its parent which is parented to another window then it has painting issues. This happens when a QTabWidget in the main window (which the first dialog is parented to) has a QTableWidget in it. If the tabs have been changed and then the dialog shown, the table widget disappears and is not repainted until the dialogs are closed.

The problem is not specific to QTableWidget, but seems to occur with any QAbstractScrollArea widget.

This is a regression from Qt 4.4.3.