Steps to Reproduce

Run fiddle:

https://zkfiddle.org/sample/19kovsi/5-frozen-tree-issue

Scroll the tree

mouse over the orange area

Current Result

Tree triggers onSize

frozen size jumps twice

Scroll position is reinitialized at the beginning of the current column

Expected Result

unrelated onResponse shouldn't cause UI jumps

Debug Information

Starting point:

zul.sel.Treechildren.prototype.onSize called by zul.sel.Treechildren.prototype.onResponse

Triggers the onSize workflow, including recalculating frozen / scrollPos

Workaround

<script><![CDATA[
    zk.afterLoad("zul.sel", function () {
        var _xTreechildren = {};
        zk.override(zul.sel.Treechildren.prototype, _xTreechildren, {
            onResponse: function() {
                //before
                //var result = _xTreechildren.onResponse.apply(this, arguments);
                //after
                //return result;
            }
         });
    });
]]></script>