Bad transient tooltip rendering

Let's say there are 2 widgets one with a short tooltip and another one with a bigger tooltip. When moving the mouse from the widget with the shorter tooltip to the widget with the bigger one, there is a transient time where the shorter tooltip text is expanded to fit the tooltip rectangle that will show the bigger tooltip.

See the attached images to have an idea of what's the problem.

The problem is very annoying since I keep seeing bad tooltip rendering when switching from one widget to the other. The transient time where the tooltip is not properly rendered can be longer on slower machines or when using the application through a remote desktop on a laggy connection.

I could reproduce this issue on Mac (10.10) with the latest version of Qt (5.4.1). It seems to me a regression, since I did not see that problem in Qt 5.3.2.
On windows it seems to work well.

Attached is a very simple example on how to reprocude the issue.