Zakaria, this is a problem I just fixed on OpenACS. I'm sure it hasn't been reflected in the dotlrn package yet.
Here's the post where I reported the same problem:
https://openacs.org/forums/message-view?message_id=194108
The fixes are in CVS. You can browse CVS via http://cvs.openacs.org
You will not have this problem is you change your installation to use the standard ports of 80 and 443. So you can either change the ports, or change your local installation with these fixes. Or you can wait until the package itself it updated.