A while ago we started using SVG images for skin icons on mobile devices. We got some positive feedback about this change as it improved the quality of the images.
Unfortunately we also discovered that the current version of cPanel blocks SVG images from being served and some of you had to downgrade to using PNGs for your icons. We have communicated this problem to the cPanel developers and they promised to fix it in the upcoming cPanel version (11.40.1).
The good news is that we found a workaround for this problem and upgraded our mobile skins so they can use SVGs even under the current version of cPanel. If you're using Roundcube under cPanel, we encourage you to upgrade your mobile skins and fix the icon problem once and for all.