Actually, the number of posts in the text Please choose the new owner of the [n] posts by... keeps increasing. From one to two to three and so on…
All you need is keep clicking on the Change Ownership button, bringing up the modal dialog, then dismissing it. It will keep adding posts to the list, even when you dismiss the dialog every time.
And worse, go out and click on another topic, and do the same. The numbers KEEP ADDING. The only way out of this is to reload the site.
Someone has forgotten to clear some array in JavaScript when the dialog is dismissed…