siri music iOS 8.4 issue

After installing iOS 8.4 on my iPhone 6, i have found an issue with Siri and the new music app. When I ask Siri to play a playlist, there is no problem; the problem happens when I ask Siri to play a song or particular artist...Siri will only play the artist or song IF i have wifi or have cellular data selected for use with music. I use iTunes Match and have over 1800 of my songs on downloaded to my iPhone. When I ask Siri to play an artist I have download on my iPhone, I get the same results.

I figured this out by turning on cellular data for Music and asking Siri to "play artist James Bay"; which is downloaded to my iPhone. James Bay played and I listened to 15 minutes. When I turned off the cellular data for Music, I noticed that 15.1 mb of data had been used! Why is cellular data being used to play songs that I have downloaded?

As a follow up, I manually played James Bay for 15 minutes with cellular data on and no data was used....it appears cellular data is used only when Siri plays artist or songs I have downloaded.