Loosing Data in Demo Account

I must not understand how the demo account works. Everytime I modify a project (not a database structure) all the previously entered data is missing.
Here's what happens -

1. I modify a project then BUILD it.
   
2. I choose DEMO ACCOUNT then the UPLOAD button
   
3. I'm taken to my project where all previously entered data is empty.
   
4. I enter new data, search, edit, everythings works and the new data is there.
   
5. I exit the DEMO ACCOUNT then return to it via VIEW ACCOUNT
   
6. All the previously entered data is there.
   
7. I exit the DEMO ACCOUNT then do 1 and 2 again.
   
8. Result is 3
   Obviously I'm missing something. Please help.