Editor not visible and/or not saving content if CiviCRM ACLs are active - but CKEditor not affected

Joomla 2.5.11, CiviCRM 4.3.5

Our users with admin permissions are able to use the Wysiwyg editor with no problems, irrespective of which editor is selected in CiviCRM or Joomla. This happens for example when composing an email, or when editing the "details" field of an activity.

Users with reduced permissions (limited to a smart group) are only able to use the CKeditor wysiwyg editor.

If the editor is set to Joomla Default Editor in CiviCRM, the editor does not display, but the editor pane accepts input. If it is set to TinyMCE, the editor does display, and accepts input. However, in both these cases, the input text is not saved. When sending an email, the email is sent OK, but the text of the email is not saved in the activity. No error message is logged, as far as I can see.

I have not been able to test this on the sandbox site, because it does not give sufficient permissions to re-create the situation.