Setting QTreeWidgetItem::foreground() back to default doesn't obey 'disabled' coloring

When setting QTreeWidgetItem font/foreground color with QTreeWidgetItem::foreground() and reverting it back to defaults with QTreeWidgetItem::foreground(columnId, QBrush()) the text color is always black even if it should be gray when the item is 'disabled'.

Reverting back to default values doesn't seem to be a documented feature, but it works for 'enabled' items, and the same QBrush() trick works for QTreeWidgetItem::background().

The attached example demonstrates the problem.