What seems to be happening here is that any over payments made to the mortgage are going on credit in your mortgage account and not actually being taken off the term or repayment amount.
This happens to alot of EBS customers, for example lodge a 10,000 to their mortgage account. This will then sit on credit on the account unless they specifically instruct the lender to take these funds to reduce the term or the monthly repayment amount. So if a customer has 100,000 of a mortgage and 10,000 in credit on the loan account then interest is only paid on 90,000. This will then alter the proportion of capital to interest in each months mortgage repayment saving you years on the loan(depending on the amount of credit in the mortgage account).
In relation to your 2nd question:
someone on a fixed rate can over pay by asking the lender to fix their repayments at a certain amount.by paying off a lump sum during a fixed term you will then be subject to penalties.