Expected behaviour:

• When I resize a docked QDockWindow manually, and afterwards resize the QMainWindow, I expect the size of the QDockWindow to remain.

Real behaviour:

• I have resized the docked QDockWindow manually. When I afterwards resize the QMainWindow, the QDockWindow's size jumps back to its original size.
• However, once I drag any QDockWindow out to be floating, this bug ceases to occur.

It seems to me, that commit https://github.com/qt/qtbase/commit/60be2fb6a13315f074c3c0b7793c38632f291e8b introduced this bug, because the internal variable QDockAreaLayout::fallbackToSizeHint gets set to false only in the QMainWindowLayout::hover method (which gets called e.g. on moving a floating window), but not on startSeparatorMove (which gets called once the user resizes a docked QDockWindow manually).

 To fix this, I think the function QMainWindowLayoutSeparatorHelper<Layout>::startSeparatorMove (or endSeparatorMove) must be modified to set fallbackToSizeHint = false.