asterisk users - Jun 2006 - voicemail suddenly exits on DTMF: a bug?

Hi,
I'm using Asterisk 1.2.1 and I noticed that the voicemail suddenly exits 
if  I press  ANY  key on  the  phone while the first or the second voice 
messages (es: vm-no.gsm or vm-youhave.gsm ) are played. I googled around 
but found nothing.
How can I solve this problem?

TIA

Giorgio Incantalupo