When using a QQuickWidget and showing a popup the popup can only be dismissed if the user clicks in the top left of the window:

The reason for this is because startup ordering is as follows:

 - When a QQuickOverlay is created, this is positioned to be the size of the contentItem, positioned to be centered within the window

 - It updates when the size of the contentItem changes

 - QQuickWidget creates the contentItem at the right size before assigning it to the window

 - At the time QQuickOverlay is created the window is of a null size
 - It has no reason to re-update until the window is resized

I've attached a screenshot from gammaray and a tiny app reproducing the issue.