Modal Dialog Titlebar not sizing properly

Modal Dialog Titlebar not sizing properly

So I just installed jQuery UI 1.11.4 alongside jQuery 2.1.4 (and before you ask, I tried it with 1.11.3 and got the same problem), and I made a modal dialog triggered by a button, but with the default settings of everything, the titlebar doesn't span the width of the dialog, as seen here:



It's not supposed to be doing that, is it?  The jQUI live demos certainly don't do that.  Is there something I'm missing in generation?  Here's my dialog code:
  1. weaponDialog = $('#weaponDialog').dialog({
            autoOpen: false,
            resizable: false,
            modal: true,
            height: 350,
            width: 300,
            buttons: {
                "Add": addWeapon,
                Cancel: function() {
                    weaponDialog.dialog("close");
                    clearWeaponForm();
                }
            }
        });

The height and width are arbitrary for the moment, until I get the dialog HTML fleshed out fully, then I'll need it to auto-adjust the width, but for now it's enough for testing.