form.setLinearOnMobile doesn't seem to work?

[mathias]

13.0d. Please consider the following snippet:

Browser.setIsHandset(true);

DynamicForm form = new DynamicForm();
form.setNumCols(4);
form.setLinearOnMobile(true);

TextAreaItem area = new TextAreaItem();
area.setTitle("Write");
area.setColSpan(2);

CheckboxItem box1 = new CheckboxItem("Box1", "Box 1");
CheckboxItem box2 = new CheckboxItem("Box2", "Box 2");

form.setItems(area, box1, box2);
RootPanel.get().add(form);

From the docs, i would expect that colspans would be ignored if i set "linearonmobile" to true, and is on a handset.

However, in the example above, it doesn't matter if i set isHandset to true or false, the two checkboxes are still rendered side-by-side.

Is this working as expected? Have i misunderstood something? Thanks.