Multiple selection across pages in a checkmarked listbox doesn't hold unless ctrl is pressed

<window>
        <zscript><![CDATA[
ListModelList m = new ListModelList();
for( int i = 0; i < 100; i++ ) {
    m.add( "Bloody mary nr " + i );
}
        ]]></zscript>
	<button label="Toggle checkmark" onClick="box.checkmark = !box.checkmark"/>
	<button label="Toggle multiple" onClick="box.multiple = !box.multiple"/>
	<listbox id="box" multiple="true" model="${m}" checkmark="true" mold="paging" pageSize="10" />
</window>