Help: DSC 1616 always turns on bypass for one zone after arming

I have a DSC 1616 unit that I installed and programmed myself. At some point, perhaps through something I did unintentionally, the system started to behave as follows: every time I arm it, it then displays "Bypass" and zone 1 is in fact bypassed. If I then clear the bypass (* 1 0 0 #), the system behaves as expected.



The mystery is that the system should only turn on bypass mode if I explicitly key in the bypass code after arming it. It's as if the zone is somehow programmed to default as bypassed, but I can't see any such mode in the installation or user manual.



I'm no expert, and I would not be surprised if I'm missing something obvious here. However, I am stumped!



Thanks in advance for any help.



Cheers,

Greg

Help: DSC 1616 always turns on bypass for one zone after arming