When using $.ajax as a deferred, the context is lost when the deferred succeeds and does its callback. Consider the following code:

var context = { foo: "bar" };
$.when($.ajax({ url: "...", context: context })).then(function(args) {
  //Where is context gone?
});

At the point of the comment, there is no trace of the original context object. It seems lost. According to the documentation, it should be in args[0], but args is holding [ returned data, "success", jqXHR ].

Now of course, in this example. it's still accessible due to its scope, but the whole point is to keep it accessible even if it gets out of scope.