Bug 48452 Widget is disposed while closing cool bar
This is the problem that is occurring in the nightly builds. There is something happening where a cool bar is attempting to layout disposed cool bar items.
bundles/org.eclipse.jface/src/org/eclipse/jface/action/ToolBarContributionItem.java
int nCurrentWidth;
		if (isLastOnRow) {
			nCurrentWidth = coolItem.getPreferredSize().x;
		}else {
			nCurrentWidth = coolItem.getSize().x;
		}
		setCurrentWidth(nCurrentWidth);
		setCurrentHeight(coolItem.getSize().y);
	}
	
	/*
	 * (non-Javadoc)
	 * @see org.eclipse.jface.action.IContributionItem#dispose()
	 */
	public void dispose() {
		
		
		if (toolBarManager != null) {
			toolBarManager.dispose();
		}
		
	}
	
	/**
	 * Updates the cool items' preferred, minimum, and current size. The preferred
	 * size is calculated based on the tool bar size and extra trim.
	 * 
	 * @param changeCurrentSize <code>true</code> if the current size should be changed
	 * to the preferred size, <code>false</code> to not change the current size