If you set some shortcuts to combinations with the meta key it does not trigger any action in yakuake.
For e.g. plasma or kwin meta key combinations work.

Reproducible: Always

Steps to Reproduce:
1. Set one combination to e.g. Meta-Shift-T
2. Press Meta-Shift-T

Actual Results:  
To the console is printed: ^X@sT

Expected Results:  
The corresponding action is triggered

I attached my shortcut config here. I set the shortcuts with the gui:
$ cat ~/.config/yakuakerc 
[Appearance]
Translucency=true

[Colors]
CurrentPalette=Forty Colors

[Desktop Entry]
DefaultProfile=Shell.profile

[Favorite Profiles]
Favorites=Shell.profile

[Shortcuts]
close-active-terminal=Ctrl+Shift+R
close-session=Ctrl+Shift+W
decrease-window-height=Alt+Shift+Up
decrease-window-width=Alt+Shift+Left
file_quit=Ctrl+Shift+Q
grow-terminal-bottom=Ctrl+Alt+Down
grow-terminal-left=Meta+Shift+H
grow-terminal-right=Meta+Shift+L
grow-terminal-top=Meta+Shift+K
help_whats_this[$d]
increase-window-height=Meta+Shift+J
increase-window-width=Alt+Shift+Right
move-session-left=Ctrl+Shift+Left
move-session-right=Ctrl+Shift+Right
new-session=Meta+Shift+T
next-session=Meta+;
next-terminal=Meta+Shift+N
previous-session=Meta+Shift+B
previous-terminal=Meta+Shift+M
rename-session=Ctrl+Alt+S
split-left-right=Meta+Shift+U
split-top-bottom=Meta+Shift+I
toggle-session-monitor-activity=Ctrl+Shift+A
toggle-session-monitor-silence=Ctrl+Shift+I
view-full-screen=Ctrl+Shift+F11

[Window]
Height=70
KeepOpen=false
ShowTabBar=false
Width=95