HTML: Iframes mixed up when back button clicked

I have a web page that cont开发者_运维百科ains two iframes. When I navigate to another back and then click the browsers back button sometimes (though more than not) the the iframes are duplicated. So I have one on the left and one on the right. Both displaying different pages. When I go back the one on the right is also displayed in the one on the left.

Is this a known issue?

Regards,

Billy