I am changing the price in the "Shares | Funds | Fixed Interest" window, but the changes aren't saving.

The details of the purchase are listed in the “Holding” subfolder. You are able to enter price information here, and this will allow calculate the value of your stocks based on this new price, however once the portfolio screen is exited, these prices will change back to the last price that was saved to the database. This allows you to do a “What if” analysis to see the values of your holdings if specific price changes occur. Updating price history is discussed in the relevant section of this knowledge base.