Steps to replicate the issue:
- Open a file page on Commons using the VisualEditor.
- Make any change to the page.
- Apply the change.
The change is made but additionally a huge amount of nonsense HTML and Wikitext code is added.
Search for all pages where this is currently not reverted: search for "<mw:slotheader>mediainfo</mw:slotheader>"
What should have happened instead?:
The nonsense code should not become added.
Other information :
I created an AbuseFilter blocking such edits to prevent further damage until this is fixed. Special:AbuseFilter/297