Steps to Reproduce

1. Open attached Excel file TabRepro.xlsx
   (this file is meant to be inefficient on update, to force processing time at server-side, but this affect regular documents as well due to network latency or processing time if a cell update affects a lot of dependents)
2. Put cursor in yellow bar (cell A2)
3. type a number (9)
4. wait for in-cell input both to be displayed
5. type tab twice quickly (tab-tab)
6. wait a moment
7. type another number

Current Result

focus is no longer in spreadsheet (might be at document end, or in address bar)

Expected Result

focus remains in spreadsheet

Debug Information

tab input sent during request processing cause the tab input to resolve as moving down the DOM tree tab order, instead of moving one cell right as expected while focusing a spreadsheet

Workaround

Javascript workaround: prevent tab from moving to next tab index when focusing a spreadsheet and zAu is currently processing

<script><![CDATA[ 
	zk.afterLoad("zss", function () {
	    var _xSpreadsheet = {};
	    zk.override(zss.Spreadsheet.prototype, _xSpreadsheet, {
	        doKeyDown_: function(event) {
	        	if(event.keyCode == 9 && zAu.processing()){
	        		event.domEvent.preventDefault();
	        		event.domEvent.stop()
	        		return null;
	        	}
				var result = _xSpreadsheet.doKeyDown_.apply(this, arguments);
				//after
				return result;
	        }
	     });
	});
]]></script>