Given multiple files with long lines, it seems like there is an issue srcolling sideways in the diff.
[How to reproduce]
Add two files with long text in one line and commit them in one changeset. Then go to the repository in rhodecode and click on the commit message. You should not be able to scoll sideways in the first diff box.
Used the repository at http://demo.rhodecode.org/Clones/fest for testing. System was Fedora Linux 16 with Firefox 11.