"Purchased" playlist titles missing

A very strange thing happened today -- I downloaded two {free} songs of the week from the store and carried on browsing. When I went to look at the "Purchased" playlist, all that was listed there was the 2 songs I'd just downloaded, no sign of the 200 + songs that were there yesterday.

Using Spotlight, I found that the songs weren't missing from my iTunes library, but they are no longer listed where they've been listed up till yesterday. As far as I know I haven't changed anything within the program. Is there any reason iTunes would take it upon itself to clean out the playlist?