asterisk users - Mar 2009 - Kewlstart - Busy signal before battery drop.

Hello all.

I have Asterisk connected to an Adit 600 channel bank with a TE110P and 
the channel bank is connected to a PBX providing dialtone to the PBX 
with fxo_ks signalling. When a call between the PBX and Asterisk 
completes there is a momentary battery drop/reversal or something that 
signals the PBX that the other side has hung up and then the PBX hangs 
up. This all works fine. However, when asterisk hangs up it also 
immediately starts playing a busy signal. My issue is that the busy 
signal begins playing before the battery drop occurs. This means that at 
the end of any calls or voicemails on the PBX there is a .5-1 second 
interval of a busy tone at the end. Is there any way to get the busy 
tone to begin *after* the battery drop? I've tried messing with the 
indications.conf file but didn't have any luck and I can't see anything 
in chan_dahdi.conf or system.conf. This same thing happens at home with 
my TDM400P so I'm inclined to think it's not exclusive to the channel 
bank. Anyone have any ideas?

Thanks

-Dave