Deleting a document with a link generates error message and doesn't update index

This is a serious bug, since it leads to incorrect query results in the frontend (in our case HST).

Usecase:

• user edits a document and links to another document, e.g. by using the linkpicker inside a Xinha field
• user saves & closes the document
• user deletes the document

result:
an error message is shown in the "delete document" dialog. However, the document node is deleted correctly. The document is neither visible in the CMS nor in the console. However, and this is the strange part, the document still shows up in the frontend when it is part of a query.

I suspect that the Lucene index is not updated correctly, and that's causing the error message, OR another bug causes the error message and the CMS never gets to updating the index.