xte called from xbindkeys is not working

I am trying to setup xbindkeys in Kubuntu, since I got a new mouse with some useless buttons. I was trying to bind the F5 key to the windows-logo button on my mouse, which I identified as c:134.

Unfortunately it does not seem to work. Here is what I do in .xbindkeysrc

"xte 'key F5'"
  c:134

This does not work. However, if I type into a terminal: sleep 10; xte 'key F5' and switch to another window, after 10 seconds the F5 key is correctly emulated (for example, it will refresh the current browser page).

It is not a problem of the key identification, either. This one will correctly launch Kate.

"kate" 
  c:134

I really don't get it, why xte won't emulate the key!

Any suggestions?

"xdotool key --delay 0 --clearmodifiers F5"
    c:134 + Release

Source: http://www.ict.griffith.edu.au/anthony/info/X/event_handling.txt (search for 'Generating X Keyboard Events')