SWT allows to reparent control between different parents. Unfortunately this does not fire any events hence the EmbeddedStage has the wrong x/y coordinates. If you now open windows like eg PopupControl relative to this

Steps to reproduce:
* Launch application
* Click on ComboBox => pop at correct position
* Click "Reparent"
* Click on ComboBox => notice the pop is a the old position
* Move 2nd shell
* Click on ComboBox => pop at correct position