Exactly as the summary says. Minecraft doesn't update it's audio output if you connect bluetooth headphones to your computer. If you connect bluetooth headphones to your computer, Minecraft will still play its sounds out of your speakers. If you disconnect them, Minecraft will be completely muted. This issue can be easily fixed by closing out Minecraft and then reopening it, but that's an inconvenience, especially for players who have to wait 10 minutes to load the launcher.