The text "<jsondata-invalidjson>" appears above the HTML textarea on test2.wikipedia.org when attempting to save an invalid JSON Schema.

Steps to reproduce:

1. Go to https://test2.wikipedia.org/w/index.php?title=Schema:HELLO&action=edit.

2. Enter "abc" into the textarea and press "Save page".

3. Observe the area above the textarea post-submission. The user ends up at a URL such as https://test2.wikipedia.org/w/index.php?title=Schema:HELLO&action=submit and the top of the page reads:

Creating Schema:HELLO

<jsondata-invalidjson>

Might be localisation cache? Dunno.

Version: unspecified
Severity: normal