After two days with a free account, on a Mac, I noticed this:

- If you mute your speakers via OS X while an advertisement is playing, it pauses the ad until you unmute your speakers.

- If you turn down your speaker volume via OS X too much while an advertisement is playing, the same behavior occurs until you turn the volume back up. This appears to be relative to the volume you were just listening to music at.

Quick fix around this; use headphones. Just take them off to ignore an ad. Or if you have a separate sound system, mute that. Annoying if you have a laptop though. This behavior doesn't occur when music is playing.