Help - IE6: pasting a URL breaks history

[DTT_11-1983]

I cannot using Ext.History on IE6 after pasting a URL.
First I open this link using IE6

http://extjs.com/deploy/dev/examples...y/history.html

then I click some tab, then I copy the current URL and then paste it. And I cannot go back or go forward anymore.
Everything work fine with firefox.
Hope someone can help me.