Comment 21 for bug 126150

Teej: "Does it cause any crashes or problems of any kind by having this option checked/unchecked, etc?" - yes, it does cause problems: when people plug in headphones, they expect external speakers to be turned off. This is controlled by the Headphone Jack Sense preference. Default behavior before Karmic was to have it off by default, which meant that plugging in headphones did not turn the speakers off.