Example:
Trajectory: >>What is the capital of France? Let me think<<
the KV cache tokens for "let me think" will have baked in them among other things "France", "Paris", "major city", "question"
Now you compact, and reuse the later tokens (suffix)
Compacted trajectory: >>Let me think<<all right, let's see<<
Now the compacted KV cache for "Let me think" will have baked in them "France", "Paris", and the model can be "that is weird, why am I thinking about France and Paris? there is nothing related in the previous context"