Markdown editor does not save (Dataloss!)

[dragotin]

On ownCloud Web with ownCloud10 (cloud.o.c): I edited a file in the markdown editor. After quite some editing, I accidentially hit the "back" button on the browser (through the keyboard, typing too fast). I had not saved manually before.

A dialog appeared that I have unsaved changes, and if I would like to save (which is good). I clicked Yes, and the markdown editor closed and I landed in the file list again, as it was expected with the back command.

Opening the document from the file list again in the markdown editor revealed that no changes were saved in the file 😿

[dragotin]

Debugging revealed that the save also does not happen in the text editor, with this error:

<?xml version="1.0" encoding="utf-8"?>
<d:error xmlns:d="DAV:" xmlns:s="http://sabredav.org/ns">
  <s:exception>Sabre\DAV\Exception\PreconditionFailed</s:exception>
  <s:message>An If-Match header was specified, but none of the specified ETags matched.</s:message>
  <s:header>If-Match</s:header>
</d:error>