If you've installed certain music apps such as TuneWiki or MixZing Player they have a setting that allows you to use your headphone buttons in their apps, but only in their apps. If you're like me I'm using bluetooth headphones and if I want to use the default music player I have to go to the TuneWiki settings and uncheck the "Override Headset Button" option, then I can use my bluetooth buttons in the default. Otherwise it would only work for TuneWiki.