Raise of Invoicenumber

Hi,

everytime i click on Generate there is given a new invoicenumber to the reservation, even when invoice is already sent.
My Client is using prepayments and his guests book month in advance.

He is currently using following workflow:

Step 1: Guest doing a reservationrequest with Solidres (There is no direct payment like Direct Debit, Creditcard, there is only Bank Wire as option)
Step 2: Solidres give a reservationnote to guest
Step 3: Client is sending a contract to guest
Step 4. If guest signs contract, Client is sending invoice INV#00001 to guest (first time invoice is generated and sent per email)
Step 5: Guest doing his prepayment
Step 6: Client want to sent updated invoice INV#00001 to guest as reminder (second time invoice is generated and sent per mail), but it is sent an invoice with an higher inovicenumber

Problem 1:
Why is at Step 6 a new Invoicenumber generated? There should be a check if already a number is generated. -> I think this should be fixed.

Problem 2
At Step3 id like to use Solidres for that, is it possible to have a button send Contract, (very similat to invoicefunction), which will sent a contract to guest.
Contract number should be reservationnumber and it should inherit same informations which inovice has.
I already created a contract_customer_pdf.php as a modified copy of invoice_customer_pdf.php and a override for edit_reservation, but i need some guidance how to implement it in Edit Reservation (Do i need a new class or can i use an existing)?

Kind Regards

Mark

I seriously second this also for another reason. In the process of designing an invoice I have to hit the 'Create' button several times to see the results of my efforts. Watching the invoice number increase with each hit is quite frustrating. I have tried the 'View' button, but that only shows the last generated invoice.

A simple solution would be to add a check box that reads 'Keep current invoice number'

Question:
How do I override 'invoice_customer.pdf'?

Best regards,
Himgoku