Can't find 9th zone on Dsc1832

I have started to install on a dsc1832, keeping the old system intact.  I see 8 zones on the dsc panel, but I have 9 zones active on my keypad!  On my dsc panel I have:

1 Door 1

2 Door 2

3 Window 1

4 Window 2

5 Window 3

6 Empty

7 Motion

8 Motion

9: Door 3 <--This is the one I cannot locate ... 

Where is the 9th zone for me to plug the konnected line into? This 9th door is working and chimes when I open and close, but I can't figure out which wires are for this door.  There is no expander card, Just a basic dsc 1832 card with the 8 zones.  Is this a weird way it was programmed by the original installer?