asterisk users - Feb 2005 - Feb 18 15:22:33 WARNING[1862]: chan_zap.c:3428 zt_handle_event: Ring/Off-hook in strange state 6 on channel 2

I have a Channelized Voice T-1 (FXO channels) configured as fxs_ks 
signalling and am getting the following messages on the console:

Feb 18 15:22:33 WARNING[1862]: chan_zap.c:3428 zt_handle_event: 
Ring/Off-hook in strange state 6 on channel 2

Does anyone have any idea what is causing this and how to fix it?  The 
mailing list archives had lots of questions, but no answers regarding 
this error message.