If any, then it would be the lower 3.
I suspect that all the other keys do work?
You could attempt doing this in the console:
App.g_kKeyboardBinding.BindKey(App.WC_PRINTSCREEN, App.TGKeyboardEvent.KS_KEYUP, App.ET_INPUT_PRINT_SCREEN, App.KeyboardBinding.GET_EVENT, 0)
Or, atleast to test that it actually works:
App.g_kSystemWrapper.TakeScreenshot()
That ought to produce a screenshot in the right directory (if it can).