The goal is getting conformance, implementation, and outreach. We do not require the user agent to buffer lost packets when the user has paused a presentation. We can also recommend some buffering. But the user can always turn off the configuration if they want to. From a user's perspective, I would expect the user agent to pause both streams.
Most tools only offer one pause button.
We don't specify what should happen in this case. Checkpoint 2.6 covers the case of synchronized content. We don't say anything about what the user agent should do when there are unsynchronized streams. We are presuming that both streams will be available at another time. Give the movie subtitles example as text that arrives over time but is not animated.