ZyXEL - spurious BUSY returned from firmware!

[egullich@taz.warp.com (Eric Gullichsen)]

I'm running a ZyXEL 1496E with 6.17 firmware and HylaFAX 4.0p1
on an Indigo running IRIX 5.3

Frequently when dialing from the U.S. to international numbers
commencing with 011649 I get a spurious busy signal from the ZyXEL
firmware. That is, I can hear the destination number ringing
but the ZyXEL returns BUSY and hangs up after the first ring.

In the log below, between 15:08:00.73 and 15:08:18.01 I can hear
the number ringing.

Can anyone recommend register settings to avoid this?
I'd be happy to disable busy detection altogether and simply timeout
on numbers that really are busy. Any ideas, please??
Please reply to eric@warp.com

Many thanks,

- Eric Gullichsen
  Warp Ltd.
  S.S. Vallejo
  Varda Landing
  Sausalito CA 94965
  FAX:  +1.415.332.8003
  Internet: eric@warp.com
  Home Page: http://www.warp.com/

-------------------------------------------------------------

Mar 25 15:07:56.75: [24991]: SESSION BEGIN 00000580 180059880006493773871
Mar 25 15:07:56.76: [24991]: SEND FAX: JOB 862 DEST 18005988000,,,6493773871# COMMID 00000580
Mar 25 15:07:56.77: [24991]: DELAY 2600 ms
Mar 25 15:07:59.36: [24991]: <-- [44:AT&B1&N0&S0*F0S18=2S38.3=1S39=0E0V1Q0S0=0H0\r]
Mar 25 15:07:59.52: [24991]: --> [2:OK]
Mar 25 15:07:59.52: [24991]: <-- [21:ATS8=2S7=45&H3&D2&C1\r]
Mar 25 15:07:59.55: [24991]: --> [2:OK]
Mar 25 15:07:59.55: [24991]: <-- [14:AT+FCLASS=2.0\r]
Mar 25 15:07:59.64: [24991]: --> [2:OK]
Mar 25 15:07:59.64: [24991]: <-- [9:AT+FLO=2\r]
Mar 25 15:07:59.65: [24991]: --> [2:OK]
Mar 25 15:07:59.65: [24991]: <-- [9:AT+FPP=0\r]
Mar 25 15:07:59.66: [24991]: --> [2:OK]
Mar 25 15:07:59.66: [24991]: <-- [9:AT+FBO=0\r]
Mar 25 15:07:59.67: [24991]: --> [2:OK]
Mar 25 15:07:59.67: [24991]: <-- [13:AT+FPHCTO=60\r]
Mar 25 15:07:59.68: [24991]: --> [2:OK]
Mar 25 15:07:59.68: [24991]: <-- [15:AT+FNR=1,1,1,1\r]
Mar 25 15:07:59.69: [24991]: --> [2:OK]
Mar 25 15:07:59.69: [24991]: <-- [9:AT+FIE=0\r]
Mar 25 15:07:59.70: [24991]: --> [2:OK]
Mar 25 15:07:59.70: [24991]: <-- [23:AT+FCC=1,5,2,2,1,0,0,0\r]
Mar 25 15:07:59.71: [24991]: --> [2:OK]
Mar 25 15:07:59.71: [24991]: <-- [7:ATM1L3\r]
Mar 25 15:07:59.72: [24991]: --> [2:OK]
Mar 25 15:07:59.72: [24991]: <-- [14:AT+FCLASS=2.0\r]
Mar 25 15:07:59.91: [24991]: --> [2:OK]
Mar 25 15:07:59.91: [24991]: <-- [9:AT+FLO=2\r]
Mar 25 15:08:00.01: [24991]: --> [2:OK]
Mar 25 15:08:00.01: [24991]: <-- [9:AT+FPP=0\r]
Mar 25 15:08:00.11: [24991]: --> [2:OK]
Mar 25 15:08:00.11: [24991]: <-- [9:AT+FBO=0\r]
Mar 25 15:08:00.21: [24991]: --> [2:OK]
Mar 25 15:08:00.21: [24991]: <-- [13:AT+FPHCTO=60\r]
Mar 25 15:08:00.31: [24991]: --> [2:OK]
Mar 25 15:08:00.31: [24991]: <-- [15:AT+FNR=1,1,1,1\r]
Mar 25 15:08:00.41: [24991]: --> [2:OK]
Mar 25 15:08:00.41: [24991]: <-- [9:AT+FIE=0\r]
Mar 25 15:08:00.51: [24991]: --> [2:OK]
Mar 25 15:08:00.51: [24991]: <-- [23:AT+FCC=1,5,2,2,1,0,0,0\r]
Mar 25 15:08:00.62: [24991]: --> [2:OK]
Mar 25 15:08:00.62: [24991]: <-- [14:AT+FLI="TESS"\r]
Mar 25 15:08:00.72: [24991]: --> [2:OK]
Mar 25 15:08:00.73: [24991]: DIAL 18005988000,,,6493773871#
Mar 25 15:08:00.73: [24991]: <-- [30:ATDT0116493773871\r]
Mar 25 15:08:18.01: [24991]: --> [4:BUSY]
Mar 25 15:08:18.02: [24991]: SEND FAILED: Busy signal detected
Mar 25 15:08:18.02: [24991]: <-- [5:ATH0\r]
Mar 25 15:08:18.25: [24991]: --> [2:OK]
Mar 25 15:08:18.26: [24991]: SESSION END