Thanks for your post.

This issue has been added to the tracker:
https://winscp.net/tracker/1602

Can you send me an email, so I can send you back a development version of WinSCP for testing?
Please include link back to this topic in your email. Also note in this topic that you have sent the email. Thanks.

When uploading a html file to AWS S3 using WinSCP version 5.12.1, WinSCP gives S3 file wrong metadata Content-Type. Or I don'k know whether it's wrong but at least it's incorrect. Here's the use case:

We have a static HTML web site hosted in S3. The bucket has static website hosting enabled and index.html is set as a default document. We'd like use WinSCP to upload/synchronize the files to the bucket. When uploading file called index.html to S3 everything is fine until we try to reach the document via HTTP. When I enter the website address to my browser, the file is downloaded instead of displayed on the page. The reason is that when WinSCP uploads the file, it sets Content-Type metadata to the file, and in our case the 'default' value is binary/octet-stream while it should be text/html.

I'm not sure whether this is a bug or is this a feature which I have configured wrongly?