The $.get() and $.post() functions ignore the type parameter if only the data parameter is omitted. In other words, the following calls all identical in effect:

$.get("foo.php", onSuccess);
$.get("foo.php", onSuccess, "script");
$.get("foo.php", onSuccess, "html");
$.get("foo.php", onSuccess, "not a valid type");

The expected behavior for this particular combination of optional arguments is not explicitly stated in the documentation, but that fact that the first call works (that data is indeed optional) would seem to imply that the others should work as well.

The problem is the conditional block in each function which "shifts" the arguments when data is omitted:

get: function( url, data, callback, type ) {
    // shift arguments if data argument was ommited
    if ( jQuery.isFunction( data ) ) {
        callback = data;
        data = null;
    }

In the calls above where a type is supplied, it is assigned to the callback parameter, which then gets "overwritten" in this conditional block. This can be easily solved by adding an extra line to the beginning of the block:

get: function( url, data, callback, type ) {
    // shift arguments if data argument was omitted
    if ( jQuery.isFunction( data ) ) {
        type = callback;
        callback = data;
        data = null;
    }

Attached is a patch against the current HEAD (r6388).