Listbox with multiple and checkmark and contextmenu

In listbox with multiple=true and a context menu on listitem, right-clicking on an item selects that item and deselects all others, then shows the context menu. Is you set checkmark=true and right-click, the item will be selected, but the others won't be deselected. This behavior is very strange for most of our users. This should probably be changed or at least a way to change this behavior should be added. Maybe sending onOpen before onSelect is enough, then you could deselect all others in your onOpen-handler if reference is not selected.

ZUL code for testing this:
<window title="listbox demo" border="normal">
<listbox width="250px" multiple="true" checkmark="true">
<listhead sizable="true">
<listheader label="name" sort="auto"/>
<listheader label="gender" sort="auto"/>
</listhead>
<listitem context="popupen">
<listcell label="Mary"/>
<listcell label="FEMALE"/>
</listitem>
<listitem context="popupen">
<listcell label="John"/>
<listcell label="MALE"/>
</listitem>
<listitem context="popupen">
<listcell label="Jane"/>
<listcell label="FEMALE"/>
</listitem>
<listitem context="popupen">
<listcell label="Henry"/>
<listcell label="MALE"/>
</listitem>
</listbox>
<listbox width="250px" multiple="true">
<listhead sizable="true">
<listheader label="name" sort="auto"/>
<listheader label="gender" sort="auto"/>
</listhead>
<listitem context="popupen">
<listcell label="Mary"/>
<listcell label="FEMALE"/>
</listitem>
<listitem context="popupen">
<listcell label="John"/>
<listcell label="MALE"/>
</listitem>
<listitem context="popupen">
<listcell label="Jane"/>
<listcell label="FEMALE"/>
</listitem>
<listitem context="popupen">
<listcell label="Henry"/>
<listcell label="MALE"/>
</listitem>
</listbox>
<menupopup id="popupen">
<menuitem label="test"/>
<menuitem label="test2"/>
</menupopup>
</window>