Web: Markdown editor passes extra text before and after content of the file

[LukasHirt]

Scenario

After opening a file with markdown editor there is passed extra text with some props like file name for example before the actual content of the file and also after it.

Screenshot

[LukasHirt]

It's not a problem with markdown editor. The problem is somewhere in the upload of files. If you create a file in the Phoenix then it doesn't pass this extra content.