Discovered when updating TinyMCE Behat editor steps (MDL-75913) edit_fields_settings.feature

When adding course custom fields using the TinyMCE Editor, text areas are not recording date when you press save.

This is not an issue when you use the Atto editor or the TinyMCE HTML editor

To recreate:

1. Login as Admin
2. Go to Site admin -> Plugins -> Text editors -> Manage editors
3. Make TinyMCE editor the primary editor
4. Go to Site admin -> Courses -> Course custom fields
5. Click 'Add a new custom field' link and choose 'Text area'
6. Enter in details making sure to pay attention to what you added and ensuring you put something in the text area fields
7. Click 'Save changes'
8. Click the settings cog to edit the custom field you just created
9. Notice the missing data from the text area fields.