Changing Next Due Date changes Hosting period dates on new invoice

I'm having the following

I register a customer to have a monthly hosting from 17th to 16th of the next month.
Invoices are generated with descriptions on those periods:

Plan X domain.com (17/01/2013 - 16/02/2013)


Sometimes I want the customer to receive the next invoice some more days later, like say, 24th, so I specify the Next Due Date.
Then, the invoice is generated some days earlier, accordingly with automation setting, BUT, the invoice product description now shows a Hosting period from the 24th...

Plan X domain.com (24/02/2013 - 23/03/2013)

...why?

The customer's hosting periods are still on 17th, I don't want them moved, I just want the NEXT invoice to be moved, and the next after that one will be as always on the 17th as I registered the product to be.

I can modify the invoice's description but is sent immediately once created.
This is confusing my customers

Is what I need done on a different way?
I just want the next invoice to be generated or due on certain time, but the customer still has the same service periods.