iPad 4 with iOS 8.1. Playing Soundcloud in Safari, switching to Twitter, Facebook, photos apps and the music keeps going for the whole track... Music library stuff always multitasks. YouTube vids in a safari tab stop when switching away from the app or switching tabs so clearly there is a limit depending on how the 'stream' is defined.
Try connecting to iTunes, backing up, then do a restore from the backup. This can also free up some storage on the device.