A backwards-compatibility issue I ran into. My code was wrong but it might help someone else...

I had something like this and it worked fine in 4.0.7:

Code:
Ext.create('Ext.Component', {
    renderTo: Ext.getBody(),

    autoEl: [{
        cn: [{}, {}, {}, {}]
    }]
});
Doing the same with 4.1.0-beta-1 generates some totally nonsense HTML.

The mistake is that my autoEl is an array. Get rid of the brackets and it works fine.