Steps to Reproduce

run this example

<zk>
    <combobox
              instantSelect="false"
              autodrop="true"
              autocomplete="true"
              onChanging='Clients.log(event.name + ": " + event.value)'
              onSelect='Clients.log(event.name + ": " + (self.selectedItem == null ? null : self.selectedItem.value))'>
        <comboitem value="Authorize" label="${self.value}"/>
        <comboitem value="Alpha" label="${self.value}"/>
        <comboitem value="Beta" label="${self.value}"/>
        <comboitem value="Beer" label="${self.value}"/>
        <comboitem value="Beef" label="${self.value}"/>
    </combobox>
</zk>

Type "a" in the input field

Wait a few seconds to make onChanging is complete.

Type "ctrl" and release "ctrl" without making changes to the input value (or other non-character keys such as ctrl, alt, num lock. etc)

Current Result

Pressing a releasing a key causes typeAhead to trigger.

Pressing a releasing "a" cause onChanging value to be sent 

onChanging: a

pressing and releasing "ctrl" causes typeAhead to trigger again, but uses the current already autocompleted value "authorize" as the input value, which in turns causes

onChanging: authorize

Note:

A different outcome of the same effect also happen if multiple character keys are pressed in sequence

For example, the sequence

Keydown: A

Keydown: U

KeyUp: A

KeyUp: U

will trigger 2 typeAhead invocations on the input when the content of the input is already "au"

The first invocation will autocomplete the input to "authorize" and send onchanging: au

the 2nd invocation will not trigger while the input value is already "authorize" and will send onchanging: authorize

Expected Result

OnChanging shouldn't trigger inconsistently when multiple keyUp events are resolved in sequence if the actual typed value didn't change in between.

Debug Information

doKeyUp_ will fire _typeahead

typeahead will store the last human-typed value into this.valueEnter_

the first invocation of typeahead stores the actual human-typed value in this.valueEnter_, then set the input value to the autocomplete string

the 2nd invocation of typeahead uses the autocomplete value currently in the input as the last human-typed value incorrectly and stores it into this.valueEnter_

When onChanging triggers, it reads the this.valueEnter_, which currently holds the autocompleted value instead of the last human-typed value.

Workaround

partial workaround: counts concurrently pressed keys, and only fire keyUp once no keys are currently held.

This prevents multiple typeAheads being sent during rapid typing, but doesn't prevent typeahead on already autocompleted value when pressing non-character keys like ctrl, alt, num lock. etc

<script><![CDATA[
	zk.afterLoad("zul.inp", function () {
	    var _xCombobox = {};
	    zk.override(zul.inp.Combobox.prototype, _xCombobox, {
	        doKeyDown_: function doKeyDown_(evt) {
	        	if(!this.keys){
	        		this.keys = new Map();
	        	}
	        	this.keys.set(evt.key, true);
	            if (!this._disabled) {
	                this._doKeyDown(evt);

	                if (!evt.stopped) this.$supers('doKeyDown_', arguments);
	              }
	            },
	        doKeyUp_: function doKeyUp_(evt) {
            	this.keys.delete(evt.key)
                if (!this._disabled && !this.keys.size) {
                  if (!this._readonly && !this._autoCompleteSuppressed) {
                    var keyCode = evt.keyCode,
                        bDel = keyCode == 8
                    /*BS*/
                    || keyCode == 46;
                    /*DEL*/
                    // ZK-3607: The value is not ready in onKeyDown, but is ready in onKeyUp

                    this._typeahead(bDel);
                  }

                  this.$supers('doKeyUp_', arguments);
                }
              }
	     });
	});
]]></script>