I don't think the bug is anything special, just another confusion the model can make from it's own context. Even if the harness correctly identifies user messages, the model still has the power to make this mistake.

Think in the reverse direction. Since you can have exact provenance data placed into the token stream, formatted in any particular way, that implies the models should be possible to tune to be more "mindful" of it, mitigating this issue. That's what makes this different.