This question is somewhat related to this thread about Sort Orders.
The line items of each occurrence are not automatically copied from the series. The reason for this is because you may not have the same line items for each occurrence. When you do copy the line items from the series however, the occurence is broken from the series since it has been changed. The occurence will therefore no longer update if you update the series.
If you updated the series price, and then press the Copy Job Items from series link in an occurrence, you will see the updated price.
Hope this makes sense.
Jason