TreeTable icon column cannot be hidden

Hi

I want to show an icon with every element. I've used the the Collapsiblefilesystemcontainer as template. The container declares 4 properties

FILE_PROPERTIES = new ArrayList<String>();
		FILE_PROPERTIES.add(PROPERTY_NAME);
		FILE_PROPERTIES.add(PROPERTY_ICON);
		FILE_PROPERTIES.add(PROPERTY_SIZE);
		FILE_PROPERTIES.add(PROPERTY_LASTMODIFIED);
		FILE_PROPERTIES = Collections.unmodifiableCollection(FILE_PROPERTIES);
		

and in the application I put

treeTable.setItemIconPropertyId(CollapsibleFoldDocContainer.PROPERTY_ICON);
		treeTable.setColumnReorderingAllowed(true);
		treeTable.setVisibleColumns(new Object[] { CollapsibleFoldDocContainer.PROPERTY_NAME, CollapsibleFoldDocContainer.PROPERTY_SIZE, 
				CollapsibleFoldDocContainer.PROPERTY_LASTMODIFIED });
		treeTable.setColumnHeadersKeys(new String[] { "name", "size", "lastm" });
		treeTable.setColumnCollapsingAllowed(true);
		treeTable.setColumnCollapsed(CollapsibleFoldDocContainer.PROPERTY_ICON, true);
		

But the table shows 4 columns: name, ico, size and last. It doesn't matter if PROPERTY_ICON is not in the visible column list, as this is the case. It doesn't matter if it is collapsed, that column is always shown.

Does anybody know how to hide it?

Thanks