Mod4 ignored?

[xorg at coreland.ath.cx]

Hello.

I'm having a very strange problem with regards to the Mod4 key.
Currently, it's mapped to the "windows" key:

$ xmodmap -pm
xmodmap:  up to 3 keys per modifier, (keycodes in parentheses):

shift       Shift_L (0x32),  Shift_R (0x3e)
lock        Caps_Lock (0x42)
control     Control_L (0x25),  Control_R (0x6d)
mod1        Alt_L (0x40),  Alt_R (0x71),  Meta_L (0x9c)
mod2        Num_Lock (0x4d)
mod3      
mod4        Super_L (0x7f),  Hyper_L (0x80)
mod5        Mode_switch (0x5d),  ISO_Level3_Shift (0x7c)

~/.xmodmaprc:
keycode 115 = Super_L
keycode 116 = Super_R
add Mod4 = Super_L
add Mod4 = Super_R

Unfortunately, I can't seem to get any wm to listen to Mod4. I can
use the following in ~/.fluxbox/keys, for example:

Mod4 Right :NextWorkspace
Mod4 Left  :PrevWorkspace

...pressing Mod4 + left or Mod4 + right does nothing. No key setting
involving Mod4 does anything.

xev shows the key event occuring (in other words, if I hold 'T',
for example, and then tap the "windows" key, a few of the fields change
for the 'T' key event - suggesting a modifier key is being pressed).

Any ideas?