Hover highlight remains on a button when a modal window is opened in response to button click

Use attached application to reproduce:

1) Click on "Msg Box" button -> A modal message box opens. The hover highlight remains on "Msg Box" button.

In Qt4, the hover highlight disappears from the button when message box opens. Trace shows that in Qt4 the "Msg Box" button gets leave event, but this doesn't happen on Qt5.