Icon buttons behaviour in Chameleon theme

We are experiencing some issues with icon buttons in our application. We have noticed that the drawing of the button starts without icon and then draws the icon, expanding the width of the button. This behaviour is almost unnoticed on fast computers but some users might find this annoying or strange.

I don’t know if there is a way to avoid this. Especially the resize of the button, which I think will solve some of our problems.

We are using Vaadin 7.5.6, but we have tested it with previous versions and different navigators (Firefox, Chrome, Safari, etc.)