Difference in behavior using parent.window.location.replace vs parent.location.replace in IE8

Question

Scenario: To change the URL of the parent window from within a cross-domain iframe.

In IE-8 parent.location.replace("http://google.com"); works fine whereas parent.window.location.replace("http://google.com"); DOESN'T works (throws Permission Denied).

Whats the difference when i do parent.location vs parent.window.location? And why is this different only in IE 8 (as both works fine in FF/Chrome)