For RadGrid, after setting EnableKeyboardShortcuts to false, I find the Up/Down keys are also disabled. However, according to your online document below, the Up/Down keys shouldn't be disabled in this case.

According the Keyboard Support online demo, these buttons should not get disabled:

"The grid also features an additional property ClientSettings -> KeyboardNavigationSettings -> EnableKeyboardShortcuts which when set to false will disable all keyboard navigation shortcuts except for the Up/Down and Page Up/Page Down keys."