When RadFormDecorator styles checkboxes, radiobuttons, buttons, etc., it hides the original elements and replace them with skinned ones that use images. Browsers on the other hand, do not print images by default - which leads to the behavior that you experience. Unfortunately there isn't much that we can do about that - whether images will be printed or not is a user setting in the browsers and it cannot be controlled by code (otherwise it would be a security hole). The only thing that I can suggest is either to disable such controls from decoration (by using the ControlsToSkip property) or as an alternative - to provide "Printer Friendly" pages where the styling of the page is done completely by CSS and without images.
All the best,
the Telerik team
Do you want to have your say when we set our development plans?
Do you want to know when a feature you care about is added or when a bug fixed?
Telerik Public Issue Tracking
system and vote to affect the priority of the items