Seems like needed extra config options for things to work smoother, such as

triggerAction: 'all',
forceSelection: true,
typeAhead: true,
minChars: 0,

Thanks.

Btw, I think either Ext4 itself or you guys independently should include the following "SuperComboBox" in the next release:
http://technomedia.co.uk/SuperBoxSelect/examples3.html