There are two issues with this.
1) The pref pane doesn't show the shortcut selected. For example, if I choose [email protected] for "Show 1Password mini", the pref pane displays cmd-shift-Å. Weird.
2) Despite this particular shortcut setting, and although it does work, hitting cmd-shift-+, which is the shortcut for zooming in when you have a Japanese keyboard, /also/ brings up 1Password mini. This particular bug is the one that kills me.