I entered Mantis #4391:

- Open Squeak3.9b-7051.image
- Make some changes to source code
- Open a dual changes browser, the new changes are in the current
  project (Unnamed1).
- From the changes browser, open a new change set, accepting the
  default name "Unnamed".

==> The changes that were in "Unnamed1" disappear from the change set.

Doing a "change sets with this method" confirms that the change has
been removed from all change sets in the image.