The analysis of the provided markdown files `issue.md` and `README.md` based on the hint regarding incorrect data type for keys in YAML metadata within markdown files has revealed the following issues:

1. **Issue in `issue.md`**:
    - **Issue:** Incorrect Data Type for Keys in YAML Metadata
    - **Evidence:** 
        ```
        - Original:
        
              class_label:
                names:
                  0: B-long
                  1: B-short

        - Returned by the server:

              class_label:
                names:
                  '0': B-long
                  '1': B-short
        ``` 
    - **Description:** The `issue.md` document explains a scenario where integer keys in YAML are mistakenly changed to strings when processed by the server. This is directly relevant to the provided hint, as it indicates a case where the data type for keys (integer vs. string) can lead to incorrect handling or interpretation of the metadata. According to YAML standards, keys can be of any type, but the processing error transforms integer keys into strings, which may result in unexpected behavior or misinterpretation of the data.

2. No issue related to incorrect data types for keys in YAML metadata was detected within the `README.md` file based on the provided snippet and the contents of the hint. The `README.md` content does not showcase or suggest any metadata keys or YAML-specific syntactic elements that could be misinterpreted or mismapped due to their data types.

These findings are aligned with the hint provided, focusing specifically on the discrepancy in data type handling for keys within YAML metadata. The first issue underscores the need for consistency and correct handling of data types for keys to ensure that metadata is interpreted and processed as intended.