CKeditor submits empty text for text fields

Steps to reproduce:

1. create a content type with a text field and a text format that uses ckeditor as editor
2. go to the form for creating a new node of that type
3. type some stuff into the text field (using cck editor)
4. hit preview to preview the content

Result

The text entered into that field is gone and doesn't appear in the preview. Looking at the HTTP request it is never sent to the server.

Remarks

• The problem is not reproducible with TinyMCE
• The same thing happens when I switch to the "plain text" format so this might be another way to test this
• fields that use the "Long text" field_type work just fine.

I've tested this with ckeditor version 3.6.0 and 3.6.2 with the same result.