Submitting modified file will cause "Failed to fetch" error

Q&A (please complete the following information)

• OS: macOS
• Browser: Chrome
• Version: 92.0.4515.107
• Method of installation: from official website
• Swagger-UI version: 3.20.7
• Swagger/OpenAPI version: 3.0.3

Describe the bug you're encountering

With an uploading file selected in the file selector, modifying the file and then submitting it will cause a "Failed to fetch" error.

To reproduce...

This can be reproduced on https://petstore.swagger.io/#/pet/uploadFile.

Steps to reproduce the behavior:

1. Create a text file by:

$ echo foo > /tmp/sample.txt

2. Go to https://petstore.swagger.io/#/pet/uploadFile
3. Fill in petId field with a random number, e.g. 123.
4. Select the file created in step 1 for the file field, i.e. /tmp/sample.txt.
5. Modify the file content by:

$ echo bar > /tmp/sample.txt

6. Click "Execute" button.

Expected behavior

The API should be called and the file should be uploaded.

Screenshots

Additional context or thoughts

Without doing step 5 (modifying the file content), the API call will be executed successfully.

Reproduce the issue at the petstore.swagger.io pet/uploadFile endpoint using the listed steps, including modifying the selected file before submitting. Trace the Swagger UI file-upload submission path and verify that the API is called and the modified file uploads successfully.