[Bug]: Error when running multimodal large models with --enable-prefix-caching

[jiyanxin]

Your current environment

The output of `python collect_env.py`

```text When I was using vllm to launch the Qwen2-VL model service, I configured the parameter --enable-prefix-caching. An error occurred when the service requested the second image. It seems that during the current use, this parameter is not compatible with multimodal large models. Do we have plans to fix this bug for compatibility in the future? ``` 

🐛 Describe the bug

When I was using vllm to launch the Qwen2-VL model service, I configured the parameter --enable-prefix-caching. An error occurred when the service requested the second image. It seems that during the current use, this parameter is not compatible with multimodal large models. Do we have plans to fix this bug for compatibility in the future?

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[DarkLight1337]

Are you using the latest version of the PR branch for Qwen2-VL? This should be fixed by a recent PR #8028

Edit: Could you show how you're inputting the images?