Header sort icon not cleared on model change

Steps to Reproduce

Run fiddle
http://zkfiddle.org/sample/1aq7fhr/2-grid-sort-style-not-cleared-on-model-change

click the update model button to load rows.
click the "click me " header to sort the rows
click the update model button to reload rows

Current Result

After reloading the model, rows are using the natural sorting direction.
However, the header still displays the last known sorting direction arrow (asc / desc)

Expected Result

direction arrow should be cleared on model change

Debug Info

Root Cause

Workaround

Extend grid such as:

public class GridEx extends Grid {
	@Override
	public void setModel(ListModel<?> model) {
		super.setModel(model);
		for (Component column: this.getColumns().getChildren()) {
			((Column)column).setSortDirection("natural");
		}
	}
}

and declare extended grid in zul or lang-addon