Itunes deleting certain songs I play

I made numerous smart playlists and for a short while everything was fine. About a month or two ago, I would double click or hit play to hear a song and itunes would delete that song from the playlist (all of a sudden it would be deleted). However, the song was still listed on the 'songs' tab. I tried making a new, duplicate smart playlist and when I did it wouldn't include the song that had been deleted. When I play songs from the 'song' tab that have been deleted from a playlist, they now disappear from my collection. However, unlike when being deleted from a playlist, it actually plays the song despite having seemingly deleted it. In addition, the song is not to be found in the 'song' tab however I can search for it and if I play the song it will play and not be deleted. After that the song will once more be listed in the 'song' tab and smart playlist and will no longer be deleted when played.

Strangely, as far as I can tell, this only happens to songs purchased through itunes in the 'pop' genre purchased before 2013 (the 2013 songs are unaffected).

Additional information: I have itunes 11.2.2.3. Computer is Windows 8.

Has this happened to anyone else? How can I fix this? There are a number of songs that have disappeared and I would like them back! Thanks in advance for any suggestions.