Гм, только что проверил сабж (альт, иксовая сессия в ru_RU.UTF-8) -- вводит; вот выхлоп xev:

FocusIn event, serial 36, synthetic NO, window 0x3800001,
    mode NotifyNormal, detail NotifyNonlinear
KeymapNotify event, serial 36, synthetic NO, window 0x0,
    keys:  0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   
           0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   
KeyPress event, serial 36, synthetic YES, window 0x3800001,
    root 0xd4, subw 0x0, time 0, (1,1), root:(1,1),
    state 0x0, keycode 203 (keysym 0xff7e, Mode_switch), same_screen YES,
    XLookupString gives 0 bytes: 
    XmbLookupString gives 0 bytes: 
    XFilterEvent returns: False
KeyPress event, serial 36, synthetic YES, window 0x3800001,
    root 0xd4, subw 0x0, time 0, (1,1), root:(1,1),
    state 0x2000, keycode 38 (keysym 0x6c6, Cyrillic_ef), same_screen YES,
    XLookupString gives 2 bytes: (d1 84) "ф"
    XmbLookupString gives 2 bytes: (d1 84) "ф"
    XFilterEvent returns: False
KeyRelease event, serial 36, synthetic YES, window 0x3800001,
    root 0xd4, subw 0x0, time 0, (1,1), root:(1,1),
    state 0x2000, keycode 38 (keysym 0x6c6, Cyrillic_ef), same_screen YES,
    XLookupString gives 2 bytes: (d1 84) "ф"
    XFilterEvent returns: False
KeyRelease event, serial 36, synthetic YES, window 0x3800001,
    root 0xd4, subw 0x0, time 0, (1,1), root:(1,1),
    state 0x2000, keycode 203 (keysym 0xff7e, Mode_switch), same_screen YES,
    XLookupString gives 0 bytes: 
    XFilterEvent returns: False
FocusOut event, serial 36, synthetic NO, window 0x3800001,
    mode NotifyNormal, detail NotifyNonlinear

PS: http://webery.altlinux.org/task/200991 -- можете проверить сами.