bug#54889: 29.0.50; shift keys can't function when using setxkbmap with custom_symbol in gnome

[Po Lu via "Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>]

bg.jheng@gmail.com writes:

> all keys work normally,
> my extra key level and group are working fine,
> but Shift_L, Shift_R are no function when i using  emacs -q in v29 .
> i saw `H-_   is indefined` in minibuffer but no any letter inserted when i tried to input any capital letter .
>
> finally, i found it can input capital letter, if i removed modifier_map of shift keys:
> in xkb_symbols file:
>     // modifier_map Shift { <LFSH> };
>     // modifier_map Shift { <RTSH> };
>    //  modifier_map Shift { Shift_L, Shift_R };
>
> my xkb files in here:
>   https://drive.google.com/file/d/19_tcP8VSeUYgG9f4zkGEbavbaBOwOLso/view?usp=sharing
>
> and using cmd:
> setxkbmap -model pc104 -layout us -symbols mysymbol
> or 
> xkbcomp .config/xkb/myxkb_keymap.xkb $DISPLAY
>
> now, emacs v29 shift key plus any letter can be inputed capital letter.
>
> because the same xkb keymap is woring normally in emacs 27, 28,
> so i am wonder if there is any difference in mechanisms of keymap in emacs v29?

A great deal has changed under the hood.

Would you please show the output of `xmodmap' with the shift key mapping
rules that you removed installed?

Thanks in advance.