Add Resource, Add Gradient, etc. buttons keep their hover effect after mouse over

When the QWidget property editor is opened in Designer, the "Add X" buttons along the top look like this:

When you hover the mouse over the buttons, they have a hover effect, but stay that way until you click somewhere and hover over them again:

The expected behaviour is that they lose their hover effect when the mouse leaves them.

I tried to see if this was a Qt issue rather than it being the fault of some custom Creator button, but I was unable to recreate the buttons or find them in Creator's source.