Steps to reproduce the issue

1. Make sure that joomla is installed in a subdirectory
2. Go to a page that loads the codemirror editor. eg the template file editor
3. Check that codemirror loads
4. Go to the codemirror plugin
5. Save and close without making any changes
6. repeat steps 2 & 3

Expected result

codemirror loads

Actual result

codemirror fails

Inspect BEFORE codemirror fails

Inspect source AFTER codemirror fails

Comments

I suspect the problems origin comes from

Note

To reset the plugin to the values before saving

INSERT INTO `h6nap_extensions` (`package_id`, `name`, `type`, `element`, `changelogurl`, `folder`, `client_id`, `enabled`, `access`, `protected`, `manifest_cache`, `params`, `checked_out`, `checked_out_time`, `ordering`, `state`, `note`) VALUES (0, 'plg_editors_codemirror', 'plugin', 'codemirror', NULL, 'editors', 0, 1, 1, 1, '{"name":"plg_editors_codemirror","type":"plugin","creationDate":"28 March 2011","author":"Marijn Haverbeke","copyright":"Copyright (C) 2014 - 2017 by Marijn Haverbeke <marijnh@gmail.com> and others","authorEmail":"marijnh@gmail.com","authorUrl":"http:\\/\\/codemirror.net\\/","version":"5.40.0","description":"PLG_CODEMIRROR_XML_DESCRIPTION","group":"","filename":"codemirror"}', '{"lineNumbers":1,"codeFolding":1,"markerGutter":1,"lineWrapping":1,"activeLine":1,"selectionMatches":1,"matchTags":1,"matchBrackets":1,"autoCloseTags":1,"autoCloseBrackets":1,"keyMap":"","fullScreen":"F10","theme":"","activeLineColor":"#a4c2eb","highlightMatchColor":"#fa542f","fontFamily":"0","fontSize":13,"lineHeight":1.2,"scrollbarStyle":"native","preview":null}', 0, '0000-00-00 00:00:00', 1, 0, '');