[STUMP] Super key doesn't work

Hello,

I've just installed StumpWM from git hub, following the instructions on 
the website. I'm using SBCL (installed from the Debian repos) as my 
lisp, with the extra libraries installed via quicklisp as recommended. 
Despite having followed the trouble-shooting instructions in 
Stumpwm.info, I still can't get Super to work in my keybindings.

I have the following in my .stumprc:

(in-package :stumpwm)
(run-shell-command "xmodmap ~/.Xmodmap")
(set-prefix-key (kbd "M-j"))
(define-key *root-map* (kbd "[") "exec emacsclient -c -n 
--alternate-editor=''")
(define-key *root-map* (kbd "]") "exec conkeror")

(define-key *top-map* (kbd "S-TAB") "fnext")

The second line runs the following through xmodmap:

remove Lock = Caps_Lock
keysym Caps_Lock = Alt_L
keycode 206 = Meta_R
keycode 133 = Super_L
clear mod4
add mod4 = Super_L

The output of xmodmap is:

tws:~$ xmodmap
xmodmap:  up to 3 keys per modifier, (keycodes in parentheses):

shift       Shift_L (0x32),  Shift_R (0x3e)
lock
control     Control_L (0x25),  Control_R (0x69)
mod1        Alt_L (0x40),  Alt_R (0x6c),  Meta_L (0xcd)
mod2        Num_Lock (0x4d)
mod3
mod4        Super_L (0x85)
mod5        ISO_Level3_Shift (0x5c),  Mode_switch (0xcb)

At this point I expect S-Tab to run fnext, but it does nothing. If I 
call it with Emacs focused, Emacs reports that s-tab is not bound.

Please help!

Thanks,

Tyler