Shift+TAB not working on mpv window, on Linux

[TheAMM]

mpv version and platform

mpv 0.28.0-562-g7d8eee3 Copyright © 2000-2018 mpv/MPlayer/mplayer2 projects
 built on Thu May  3 01:38:48 EEST 2018
ffmpeg library versions:
   libavutil       56.15.100
   libavcodec      58.19.100
   libavformat     58.13.100
   libswscale      5.2.100
   libavfilter     7.18.100
   libswresample   3.2.100
ffmpeg version: N-90776-gfbfee6a

On Ubuntu (Ubuntu 14.04.5 LTS, yes, old), with lightdm or gnome or whatever the desktop is called. IRC also confirmed the same for an xfce desktop and Linux Mint Cinnamon.

Reproduction steps

Open mpv with mpv --idle --input-test --force-window, press Shift+TAB (with focus on the mpv window)

Expected behavior

Console prints

[input] Key Shift+TAB is bound to:
[input] (nothing)

Actual behavior

Nothing is logged in the console. TAB works, Ctrl+TAB works, but Shift+TAB will not show.
Focusing on the terminal and pressing Shift+TAB will work, but focusing the window won't.

Log file

https://0x0.st/s2-P.log (the TAB presses are plain TAB presses, to show that key events are handled at all)

I don't think X11 even has a way to signal whether a key was "consumed" or not. WMs either have to grab keys globally, or accept the facts that applications get them when their window is focused.

Nevermind, I confused something. Can reproduce.

[TheAMM]

Forgot to mention that xev does display the events (shift-down, TAB-down, TAB-up, shift-up)

KeyPress event, serial 37, synthetic NO, window 0x3e00001,
    root 0xc0, subw 0x0, time 863492285, (-17,506), root:(795,558),
    state 0x0, 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 0x3e00001,
    root 0xc0, subw 0x0, time 863492898, (-17,506), root:(795,558),
    state 0x1, keycode 23 (keysym 0xfe20, ISO_Left_Tab), same_screen YES,
    XLookupString gives 0 bytes: 
    XmbLookupString gives 0 bytes: 
    XFilterEvent returns: False

KeyRelease event, serial 37, synthetic NO, window 0x3e00001,
    root 0xc0, subw 0x0, time 863493007, (-17,506), root:(795,558),
    state 0x1, keycode 23 (keysym 0xfe20, ISO_Left_Tab), same_screen YES,
    XLookupString gives 0 bytes: 
    XFilterEvent returns: False

KeyRelease event, serial 37, synthetic NO, window 0x3e00001,
    root 0xc0, subw 0x0, time 863493630, (-17,506), root:(795,558),
    state 0x1, keycode 50 (keysym 0xffe1, Shift_L), same_screen YES,
    XLookupString gives 0 bytes: 
    XFilterEvent returns: False

Although the keysym is different from what plain TAB and Ctrl+TAB show:

KeyRelease event, serial 37, synthetic NO, window 0x3e00001,
    root 0xc0, subw 0x0, time 863670464, (-577,366), root:(235,418),
    state 0x4, keycode 23 (keysym 0xff09, Tab), same_screen YES,
    XLookupString gives 1 bytes: (09) "	"
    XFilterEvent returns: False

---

Edit Oh, during the time I'm typing the backticks, wm4 goes and fixes it.

Yeah, I looked at xev output too.

[haasn]

λ xmodmap -pk | grep Tab
     23    	0xff09 (Tab)	0xfe20 (ISO_Left_Tab)	0xff09 (Tab)	0xfe20 (ISO_Left_Tab)	

God only knows why xmodmap binds shift+tab to a different tab (?) by default, but that does mean a work-around exists:

λ xmodmap -e 'keycode  23 = Tab Tab Tab Tab'
λ mpv --input-test --force-window --itle
     input: Key Shift+TAB is bound to:
     input: (nothing)

(Seems like a proper solution would be teaching mpv that ISO_Left_Tab = Tab, obviously)