It looks like IE8 now supports the hashing mechanism which is used to record history, just as is done for non-IE browsers. Therefore, I don't think IE8 needs to use the iframe (unless compatibility mode is switched on).
Perhaps History.js could be updated to replace all the occurences of:
I have overridden Ext.History in this way, and all seems fine. (Without this override, Ext.History fails in IE8 when a DOCTYPE is used).Code:if (Ext.isIE && !Ext.isIE8)