Field properties box disappears after changing the Path property

• generate project using archetype
• run cms and log in as admin
• browse to documents > configuration
• open 'textdocument' in document editor
• click edit
• click on Title field
• in properties box (bottom right) change the value of Path, e.g. from "title" to "header"
• click in the Caption field to edit that too from "Title" to "Header"

The moment you click in the caption field, the complete properties box disappears. You have to click on the Title field to get it back again.