Why key snooper response twice on one key press?

[Magicloud Magiclouds <magicloud magiclouds gmail com>]

Dear,
   I am using gtk_key_snooper_install. In the call back function, I 
just print out the keyval and state, then return TRUE.
   While the application running, I hit 'a', and I got '0x61 0x0' 
twice. Why it is like this?

Thanks.