Maybe this helps, I bought several names in one package for a discount and of course had the same worry that you had. I was assurred that all reg fees ones negotiated and regged will always be the same. A few months later after some new names I asked the same question in a different way (just to be sure) and got the same answer, this time with the word 'forever', so I wouldn't be too worried about it. It is also a strange thing to do, but if this has happened to someone here or will happen later on, please let me know as I will confront this contact, but I am sure you don't have to worry.

Edit: However, like Equity is saying, if a name is dropped or still free to register, they can do whatever they want with the reg fee.