A customer bought a house and needed a bathroom fan and heat lamp. I replaced the bathroom outlet with a GFI and tapped of of it for the fan and light only to discover the circuit was dead! I was pretty sure I hadn't cut or drilled any existing wires. I had continuity on the ground but nothing neutral to ground or hot to ground. I started looking for a GFI. Took about an hour to find it under the new deck. some time in the past someone wanted to save a few bucks (GFI's were expensive way back when) and protected the bathroom receptacle with the outdoor GFI. What a pain in the a**!
bob

Elecbob:
My favorite is the new houses, 400 to 600K.
3 or 4 baths, 1 GFI; guess where?? Usually the first floor bath.
Second is the exterior and garage receptacles, trip the GFI, and you have to run down to the basement; they're tied into the basement (unfinished) gfi.
The "inexpensive" way to satisfy the '99 code.
NJ still is under the '99 NEC, hopefully the State will apopt the '02 NEC before the '05.
The required update course is getting tougher to remember being that we don't use it yet.
John