I realize this is a really old thread, but I have landed on it multiple times when trying to figure out the same issue. Each time, I have figured it out, but forget how I did it. Anyway, this reply is to remind me later, as well as anyone else who lands on it as I have.
The DHCP field is required because the DHCP server is enabled in the "Global" tab.
The FIRST and MOST IMPORTANT step is to run TftpdXX (32 or 64) as Administrator. If you don't know how to do this, look it up. Not running it as Administrator will cause your settings not to save. This is all provided that you are running UAC. If you aren't running UAC, then just do the following.....
Click on Settings:
Then click on the Global Tab and uncheck "DHCP Server":
Make any other changes that you would like to be standard and click "OK". These settings will then be saved and loaded each time you open it.
You will need to restart the program for the changes to take effect.
I hope I've helped someone. (mainly me later) LOL