ExtJS.Bugs

ext-2.0.2\source\util\MixedCollection.js:83-84

var old = this.map[key];
if ( old ) {

Will fail if false boolean values (or other falsey values) are stored in the collection.

Suggested fix:

var old = this.map[key];
if ( typeof old !== "undefined" ) {

c[c.length] = {key: k[i], value: items[i], index: i};

Two scripted operations instead of one. Why?

Suggested fix:

c.push( {key: k[i], value: items[i], index: i} );

Why aren't the "private" functions '_sort' and 'createValueMatcher' stored in a closure? Rather they are exposed as part of the public interface.