AJAH text vanishes when "adding another item"

Steps to reproduce:

1. create a content-type with a text-field that allows an arbitrary number of values.
2. go to the node creation form
3. put some text into the first instance of that text-field
4. press "add another item"

Result:
A second text field appears. The text that was entered into the first field has vanished.

It seems that WYSIWYG fails to put the text entered into the original textarea before the AJAX request is sent.