For some inexplicable reason the capital d key on my Ubuntu system is no longer producing output. Hitting caps lock and then d produces a D. I've tried multiple keyboards and the issue is the same. There's nothing bound to Shift+d under System > Preferences > Keyboard Shortcuts. xev produces the following:

shift + a

KeyPress event, serial 36, synthetic NO, window 0x4c00001,
    root 0x27a, subw 0x0, time 31268952, (130,-16), root:(1000,525),
    state 0x10, keycode 62 (keysym 0xffe2, Shift_R), same_screen YES,
    XLookupString gives 0 bytes: 
    XmbLookupString gives 0 bytes: 
    XFilterEvent returns: False

KeyPress event, serial 36, synthetic NO, window 0x4c00001,
    root 0x27a, subw 0x0, time 31269376, (130,-16), root:(1000,525),
    state 0x11, keycode 38 (keysym 0x41, A), same_screen YES,
    XLookupString gives 1 bytes: (41) "A"
    XmbLookupString gives 1 bytes: (41) "A"
    XFilterEvent returns: False

KeyRelease event, serial 36, synthetic NO, window 0x4c00001,
    root 0x27a, subw 0x0, time 31269584, (130,-16), root:(1000,525),
    state 0x11, keycode 38 (keysym 0x41, A), same_screen YES,
    XLookupString gives 1 bytes: (41) "A"
    XFilterEvent returns: False

KeyRelease event, serial 36, synthetic NO, window 0x4c00001,
    root 0x27a, subw 0x0, time 31269608, (130,-16), root:(1000,525),
    state 0x11, keycode 62 (keysym 0xffe2, Shift_R), same_screen YES,
    XLookupString gives 0 bytes: 
    XFilterEvent returns: False

shift + d

KeyPress event, serial 36, synthetic NO, window 0x4c00001,
    root 0x27a, subw 0x0, time 31102792, (115,-13), root:(985,528),
    state 0x10, keycode 62 (keysym 0xffe2, Shift_R), same_screen YES,
    XLookupString gives 0 bytes: 
    XmbLookupString gives 0 bytes: 
    XFilterEvent returns: False

FocusOut event, serial 36, synthetic NO, window 0x4c00001,
    mode NotifyGrab, detail NotifyAncestor

FocusIn event, serial 36, synthetic NO, window 0x4c00001,
    mode NotifyUngrab, detail NotifyAncestor

KeymapNotify event, serial 36, synthetic NO, window 0x0,
    keys:  2   0   0   0   0   0   0   64  0   0   0   0   0   0   0   0   
           0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   

KeyRelease event, serial 36, synthetic NO, window 0x4c00001,
    root 0x27a, subw 0x0, time 31103104, (115,-13), root:(985,528),
    state 0x11, keycode 62 (keysym 0xffe2, Shift_R), same_screen YES,
    XLookupString gives 0 bytes: 
    XFilterEvent returns: False