Daughter of Madain Sari is pretty much a mix of Eiko's Theme and Melodies of Life. Garnet's Theme also partially uses the melody of Melodies of Life.

Protecting My Devotion, Loss of Me and Rose of May (notice also the similar-sounding names of the latter two) are also variations on the same melody.

They do this a lot in the game. It's pretty interesting to look for connections, since they're never randomly the same. The music has a connection, generally, when the situations they're played in are connected.