frame and imp 2.0.2.8

[Imp User]

Dear all,

I've used imp for 6 months and it's great. Thanks for all the developers
on this project!!

I have a frame problem and the situation is as follows:

1. I login to imp say http://mail.horde.org/imp 
2. I can read 4 frames including the main 
3. Then I browse to other sites say www.yahoo.com
4. I return to http://mail.horde.org/imp
5. All the 4 frames can be seen
6. When I click INBOX on the left bar, problem occurs : 4 frames becomes
only one frame and all the menu bars disappear.

I've tested it with IE 5.5 and netscape 4.75 and both have problem.

Please help...

thanks and regards,
Boris