This may be a feature to ensure continued payment, many Pay-Per-View services will block viewing after a certain period, DMR or Digital Media Rights licensing is applied to the files, these are only licensed for a certain period of time and usually as soon as the license has expired, you'll need to download a new licensed file.
Sometimes DMR is not the case, sometimes this is a programming limit set by the developers.
Usually the correct way to update the XML List View, would be to increment an array by each addition and display the total items in the array.
However, some developers take in to consideration - the time it takes to select each item for removal..
If you saved 500 items, the list would take hours to navigate and also take forever to clean up/remove items, it is easier to limit the list length than to have search functions alongside multi-select items.
Some ROOT Access applications will let you stream your system audio into an mp3 file, this would let you Back them Up.