Since we are using a sprite image to include all the icons, this image is usually cached by browsers.
When the portal upgrades to a new version, the sprite image with the icons change, but the name is kept the same; therefor users will still have the old one in their cache and will see wrong icons everywhere (for example, a printer icon in "edit" or a trash icon in "view"). Users need to clean their browser cache so that they get the latest sprite image with the icons in a nice way.
We should have a mechanism to detect that the image has changed and load the latest one. For example, we could use the "t" parameter we use for many other images in the portal, so that the browser always ask for the latest one.