Thank you for reporting this bug. We will make it our priority to review this report.
Sencha Premium Member
Bug in Ext 4.1.3 exception inHeader.afterLayout
On line 185 of src/panel/Header.js in afterLayout
titleEl = me.titleCmp.el;
I occasionally get an exception where titleCmp is undefined. This happens when me is a Bar (src/tab/Bar.js). Bar is a subclass of Header. You'll notice in Bar's initComponent it deletes titleCmp:
So it will fail for Bar when it calls the parent's afterLayout. I suspect you should check for titleCmp in Header's afterLayout to fix the bug