Problem detecting sit

I have a problem with detecting when an avatar sits. I cut from the wiki changed event, and eventually pared it down to this to see if it actually detects anything.

default
{
    state_entry()
    {
    }
    
    changed(integer change)
    {
        if (change & CHANGED_LINK)
        {
            if (llAvatarOnSitTarget() != NULL_KEY)
                {
                    llOwnerSay("someone sit down?");
                 }
            else if (llAvatarOnSitTarget() == NULL_KEY)
                {
                    llOwnerSay("someone stood up?");
                 }
            else llOwnerSay("woops");
        }
      
    }

}

Whether I sit down on or stand up from the object, I always get the second message, "someone stood up?". How do I get it to detect when I actually sit down???

Thanks,
Baron