Clear user input doesn't sent a onChange and onSelect

Steps to reproduce

1. load zul

   <zk>
   <div apply="org.zkoss.bind.BindComposer" viewModel="@id('vm')@init('support.customization.T2407VM')">
   <combobox model="@load(vm.model)" selectedItem="@bind(vm.ourProp)"/>
   <button onClick="@command('onChange')"/>
   </div>
   </zk>
   

2. select an item in the combobox with a mouse
3. clear the item by pressing the "backspace"
4. press the tab to blur it (or click outside from the combobox)

Actual result

no event sent. So selectedItem on the server doesn't change. But ZK 7 will send events below:

dtid:z_y_90
cmd_0:onChange
uuid_0:z_3
data_0:{"value":"","start":0}
cmd_1:onSelect
uuid_1:z_3
data_1:{"items":[]}

Debug info

• in step 2, if selecting an item with the up and down key. Events are sent.