Markup field value is saved as string "Array"

As in title. To reproduce:
1. create new form
2. add markup field
3. type anything in value textarea
4. save

In the editor as well on view form page the field is displayed as "Array" string (PHP array was cast to string?). Editing such field is impossible (saving fails). I have WYSIWYG module with ckeditor 3.0, didn't try it with WYSIWYG editor turned off.