Another possible module bug ... though perhaps one not worth fixing. Create a document and add a module like Endnotes. Checking the latex source, merely adding the endnotes module doesn't change anything yet: you have to add an endnote, and only then does the \usepackage{endnotes} line get added to the preamble.
However, if you add an endnote within a LyX Note (and nowhere else in the document), the endnote will not appear in the LaTeX output, and yet the \usepackage{endnotes} line is added to the preamble anyway -- unnecessarily. Should this not happen? Bennett