[KevinH]

Okay, creating links to the top of the page in the nav from the top of the page in the nav via EditTOC was not a case we had considered. I have now pushed a fix for this to master.

FWIW, a better way to handle this would be to specify the target with a proper fragment from the list that is provided. Linking to the nav toc from the nav toc is not common.
Hand adding a new target that does not exist in the list of potential targets is also probably not the best idea.

If you do hand add a new target in this case, the nav.xhtml has id="toc" that it would make for a better target id than the top of page for the nav itself.

Thank you for your bug report.