Issue with Multiple File Reference Errors in Spine

[byword]

I verified that the Spine error occurs after building version 2.8.1 with the latest code pulled from Git. This error is consistently reproducible.

Sigil Version: 2.8.1 (built directly from git source)

Sample error code

<spine toc="ncx">
<itemref idref="Section0001.xhtml"/>
<itemref idref="Section0003.xhtml"/>
<itemref idref="Section0004.xhtml"/>
<itemref idref="Section0005.xhtml"/>
<itemref idref="Section0002.xhtml"/>
<itemref idref="Section0004.xhtml"/>
</spine>

Steps to Reproduce:

1. Create a new ePub file.
2. Add multiple XHTML files.
(e.g., In the Section0001.xhtml file, press Ctrl+Enter multiple times to split it into Section0002 through Section0007)
3. In the Book Browser, select non-adjacent files
(e.g., select Section0002, Section0004, and Section0006 with non-contiguous selection).
4. Drag and move the selected files below Section0007.


After performing these steps, Section0004 and Section0006 appear duplicated in the Spine. While the Spine entry is added to the new location after moving the files, the original entry in its prior location is not removed.

The attached sample.epub file is the resulting file after performing these steps.