Created attachment 54799 [details]
Demo of undesired deletion of bookmarks

PREAMBLE:
The attached document is a very simple specimen "academic paper" in which references (to other papers), indicated by numbers in square brackets, are resolved in a Table at the end of the document.  

The author's intention is (i) to create references in arbitrary order, as they occur when writing the document.  Just before publication, the references are to be sorted (ii) into alphabetical order of lead author.  The Table of References is to be automatically renumbered (iii), and the references in the text of the document are to be renumbered accordingly (iv).  This is a reasonable and standard requirement in writing such a document.

Each reference in the Table of References is indexed by a Field of type Number Range.  This is in order to facilitate the renumbering of references at step (iii) above.  For each reference in the Table, the reference number is bookmarked.  The bookmark is used to insert the reference number into the main text of the document.

Just before publication, the author selects the entire Table (Table, Select table) and sorts in on column 2.  Selecting the first column of the table, and updating the fields (<F9>, or Tools, Update Fields), causes the desired renumbering both in the Table and the main text of the document.

So far, so good.

THE BUG:
If the author then selects Edit, Undo sort table, all the bookmarks are lost.

CONSEQUENCES:
These are likely to be severe.  This technique is typically used in long and complex documents with a large number of references.  The impact would be felt close to a publication deadline, and the information loss incurred would make recovery difficult.