The commands will disable the buttons if the command cannot be executed. For example, if you are on the first page, the previous page command button will be disabled, because the PreviousPage command cannot be executed. The command will enable the button once you have flipped at least one page.
If that is not the case, you can try calling the CommandManager.InvalidateRequierySuggested method, which will force all of the commands to reevaluate themselves.
the Telerik team