I have a (fairly) simple award ticket with a stopover . . .

PIT/LAX
LAX/SFO
SFO/PIT

I needed to tweak the dates a little, but the exactly the same routing. Not sure if it matters, but, I was doing this from gogo on the plane . . .

1) Check availability - all available.

2) Bring up my reservation. Click "CHANGE". Select my new flights.

Screen says - 25K miles exchange for 25K miles - perfect.

Screen says - taxes $10 paid new ticket $10 - perfect.

Zero miles and zero $$$ due.

All is good, right? ERROR! Please enter the security code for your credit card number! Why do they need my security code if it's an even exchange?!?

3) Okay, I entered my security code. Click "PURCHASE"

ERROR! "Let's try that again"!

Rinse / Repeat - 2 more times - SAME THING! ERROR.

My conclusion is that DL.com doesn't handle award tix with stopovers well, as this wouldn't book online in the first place at the right mileage!

Anyway, I'm in MEX, so I was worried that by the time I got all the way to my hotel and get my laptop and Skype connected to call, the "LOW" inventory would disappear. Luckily, it didn't.