I was surprised to find that ctrl+click does not work in the inbox in the popular Safari browser on MacOS. Shift+click works fine, just not ctrl+click. Works fine in Firefox and IE. Also, the scrollbar does not work in the inbox list surprisingly. I can see the bar, but it just won't move. I'm using the latest release of Safari on Mac OSX Tiger and the latest stable beta of RoundCube.
If you want to really screw up the interface, try sending yourself an HTML email using <DIVS> to layout the page. All of the graphics end up in the upper-left-most corner of the browser window behind the roundcube logo. This seems to be true across IE and Firefox.