This is caused by a bug in jQuery.Callbacks:

> cb = $.Callbacks()
> cb.add(function () { console.log('one'); cb.add( function () { console.log('two' ); } ); } );
> cb.fire()
one
two

What happens is:

• execute() is called for module A
• This calls addEmbeddedCSS( cssA, cbA ) where cssA is the CSS for module A, and cbA is a callback that is added to the CSS callback list
• From a timeout, addEmbeddedCSS() flushes its buffer and fires the callback list, so cbA is called
• cbA executes module A's JS
• cbA calls handlePending(), which notices that module B (which depends on A) is now runnable
• execute() is called for module B
• This calls addEmbeddedCSS( cssB, cbB ) , and adds cbB to the CSS callback list
• Once this stack rolls back up, we end up back in callbacks.fire(), which notices the newly added cbB callback and calls it immediately
• cbB executes modules B's JS
• From a timeout, addEmbeddedCSS() adds module B's CSS