[STUMP] The mode-line doesnot appear automatically on float group ?

[z_axis]

I have the following code snippet in ~/.stumpwmrc:

(if (not (head-mode-line (current-head)))
     (toggle-mode-line (current-screen) (current-head)))

("s-b" "mode-line")
...


The mode-line appears automatically on other group except the float  
group.  I must press "s-b" twice to make it appear in float group.

How can i make it appear automatically on float group ?

Regards!