I've encountered an issue while using GNU Parallel to process a large JSONL file containing very long lines. The command I'm using is:

```bash
parallel -a data.jsonl -j 64 --pipepart --block -1 -k "python process.py"
```

The goal is to process each JSON line in parallel using a Python script. However, I've noticed that occasionally, the Python script encounters json.decoder.JSONDecodeError, indicating corrupted JSON data.

*Observations:*

• *Input data integrity:* The original JSONL file is verified to be well-formatted.
• *Discrepancy in input and output:* When the Python script fails, the line causing the error is indeed malformed. This suggests that the data is being corrupted during the parallel processing.
• *Reproducibility:* To isolate the issue, I've created a simplified script (`run_tests.sh`) that merely `cat`s the input file using `parallel` and compares the output with the original using SHA256 sums. The script demonstrates that the output is not always identical to the input, even when using a simple `cat` command.
• *Environment:*

  * GNU Parallel 20241122
  * Ubuntu 20.04
  * Perl 5.30.0 and 5.40.0
  * Bash and Zsh
  * Locale: en_US.UTF-8

• *Reproducible test case:* I've created a GitHub repository containing the `run_tests.sh` script and a sample input file. Running `bash run_tests.sh test.input 1000` will execute 1000 tests and report any discrepancies.

Script and test inputs to reproduce the bug: https://github.com/pluiez/reproduce-gnu-parallel-bug