Child windows are no longer hidden when the parent window is minimized

In Qt 5, child windows are no longer hidden when the parent window is minimized.

(Qt 4.* automatically hides child windows when the parent is minimized.)

Windows: Qt 4 minimizes transient children, Qt 5 does not
XCB: Qt 4 and 5 minimize transient children (using WM properties, should work for sane WMs)
Mac: Neither Qt 4 nor 5 minimize transient children