Fedora Linux 28: Something is stealing certain key combinations. When I visit http://en.key-test.ru/ I can activate CTRL-SHIFT-ALT-q but not CTRL-SHIFT-ALT-d

I have tried in both Firefox and in Chrome.

I went through my keyboard shortcuts, and there are no shortcuts defined for CTRL-SHIFT-ALT d. I can temporarily make CTRL-SHIFT-ALT-d activate an application.

When I run xev, I see the following when pressing CTRL-SHIFT-ALT-d:

KeyPress event, serial 34, synthetic NO, window 0x3200001,
    root 0x2ac, subw 0x3200002, time 2322960, (53,48), root:(1015,177),
    state 0x10, keycode 37 (keysym 0xffe3, Control_L), same_screen YES,
    XLookupString gives 0 bytes: 
    XmbLookupString gives 0 bytes: 
    XFilterEvent returns: False

KeyPress event, serial 37, synthetic NO, window 0x3200001,
    root 0x2ac, subw 0x3200002, time 2326560, (53,48), root:(1015,177),
    state 0x14, keycode 50 (keysym 0xffe1, Shift_L), same_screen YES,
    XLookupString gives 0 bytes: 
    XmbLookupString gives 0 bytes: 
    XFilterEvent returns: False

KeyPress event, serial 37, synthetic NO, window 0x3200001,
    root 0x2ac, subw 0x3200002, time 2328408, (53,48), root:(1015,177),
    state 0x15, keycode 64 (keysym 0xffe7, Meta_L), same_screen YES,
    XLookupString gives 0 bytes: 
    XmbLookupString gives 0 bytes: 
    XFilterEvent returns: False

FocusOut event, serial 37, synthetic NO, window 0x3200001,
    mode NotifyGrab, detail NotifyAncestor

FocusIn event, serial 37, synthetic NO, window 0x3200001,
    mode NotifyUngrab, detail NotifyAncestor

KeymapNotify event, serial 37, synthetic NO, window 0x0,
    keys:  4294967212 0   0   0   32  0   4   0   1   0   0   0   0   0   0   0   
           0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0

If I run CTRL-SHIFT-ALT-q, i don't see the FocusOut/FocusIn/KeymapNotify events.

How do I fint out what is stealing/modifying my key presses?

A co-worker of mine has seen the same phenomenon when using Ubuntu.