Bengt,

I realize this post is a few months old so you probably have moved on from this question or have already found the answer. I just figured I would post back since I ran across this same issue yesterday in Word 2010.

I have a document with three buttons. The three buttons call userforms that have textboxes on them. The click events for the OK buttons of the userforms update bookmarks in the document. When setting the text of the bookmarks, the bookmarks are automatically deleted.

The Layout properties of the three buttons in the document are set to be "In Front of text" which makes them part of the Shapes collection in the document. Each Shape is anchored to a paragraph in the document. If you toggle the Show/Hide button in the Paragraph section of the Home ribbon, you will be able to see an anchor next to the paragraph to which the Shape is anchored.

In my case, my buttons were anchored to a paragraph that was a bookmark to be updated. When the bookmark got updated, it deleted the bookmark, as well as the button that was anchored to the paragraph. Sorry this is a little long, but I hope it helps you or someone else that might be having the same issue.

Best regards,
Snooklepig