.attr('name', undefined) returns attr value instead of current set

[oraz]

.attr() returns attribute value instead of current node set if the second argument is undefined. Code to reproduce:  http://jsfiddle.net/oraz/zDNCb/

In the following examples .attr() returns current node set:

1. when we pass object like {someAttr: undefined} as only argument:  http://jsfiddle.net/oraz/aBnb4/
2. when we pass null as the second argument:  http://jsfiddle.net/oraz/3frQB/

Environment:

• jQuery 1.6.4
• jQuery 1.6.2
• Firefox 7
• Google Chrome 14
• IE 8

Possible fix at line 1956:

attr: function( name, value ) {
   if(arguments.length == 2 && value === undefined) {
        value = null;
   }
   return jQuery.access( this, name, value, true, jQuery.attr );
}

[rwaldron]

Duplicate of #9427.

[oraz]

Why the issue was closed?
What's the difference between the following examples?

$('body').attr({someAttr: undefined}).each(function() { alert('Hello'); });

$('body').attr('someAttr', undefined).each(function() { alert('Hello'); });

As for me, these examples are identical, but the first works fine and the second one doesn't work. It means that .attr() (.css(), data(), etc...) method returns different result even if I pass actually the same attr name and value.