selecting an item doesn't deselect others with a mobile device

Steps to Reproduce

1. visit the zul with chrome device simulator, iPad

    <listbox id="lb" width="150px"
             multiple="true" checkmark="false">
        <listitem forEach="1,2,3,4,5" label="item ${each}"/>
    </listbox>

2. select 1st item
3. select 2nd item

Current Result

both items are selected

Expected Result

only the 2nd item is selected

Debug Information

• with a desktop browser, this issue doesn't happen
• ensure that the spec is "if no checkmark, selecting one item will de-select others, on desktop and mobile browsers.

Workaround

• override zul.select.SelectWidget._doItemSelect()

  if (evt.data.ctrlKey || evt.data.metaKey || (zk.mobile && !this.getCheckmark()))