The div is invisible, I used the web tools to highlight it. If it is over a button however, it prevents clicks etc.
I can inspect the element and see if is part of the TabLayoutPanel as shown in the picture below :
If anybody comes across this and needs a fix, I execute this in the onload of the widget containing the tab layout paneltabPanel.getElement().getFirstChildElement().getStyle().setProperty("top","-10000ex");Not pretty, but necessary it seems.