Bitbucket 5.3 doesn't render HTML files with .md extension

Problem Definition

Bitbucket 5.3 and 5.4 don't render HTML files with .md extension. Up to version 5.2, any .md file seems to render HTML. The problem seems to start after 5.3 version:

Versions prior to 5.3 can render HTML tags in any files (if they have the .md file extension):

Steps to Reproduce

1. Push any .md extension file with some HTML tags.
2. Open the file in Bitbucket Server