By default when you open the Portfolio page the system uses real-time market data. However, the data is not then automatically refreshed.
To see the current data for your selected rate feed you must click the Refresh button. This updates all the market data displayed in the page with the exception of any fixed rates that you have manually edited. That it, if you have manually edited a fixed rate on the page, it is not refreshed when you click the Refresh button.
In addition, it tells the system to refresh the data in all the market data pages if you had previously frozen the rates there.