%this gets lost

Sometimes in the onUpdate callback, %this loses its reference.

For example,

function npcship::fireMissile(%this)
{
   //snip 

   %this.schedule(%this.fireDelay(), "fireMissile");
}

function npcship::fireDelay()
{
   //%this gets lost here for some reason - can't use ship.firerate
   %rate =$player.fireRate * 1000;
}

The work around is to use a global variable but its not ideal. Is this a known issue or is it just me?