[Doitsu]

Originally Posted by v_x

The right order in [the] content.opf file:

<spine toc="id6">
    <itemref idref="main.xhtml" />
    <itemref idref="epi.xhtml" />
    <itemref idref="lanc1.xhtml" />
    <itemref idref="schm.xhtml" />
    <itemref idref="fund.xhtml" />
    <itemref idref="mikh.xhtml" />
    <itemref idref="mikh-notes.xhtml" />
    <itemref idref="zab.xhtml" />
    <itemref idref="zab-notes.xhtml" />
    <itemref idref="notes-lanc.xhtml" />
    <itemref idref="about.xhtml" />
</spine>

I've opened and saved your test file with the 0.8.9 Windows and Linux Sigil versions and the spine order hasn't changed. It is therefore rather unlikely, though not impossible, that the OSX version behaves differently, unless there's something strange about your file.

EDIT: If you manually edit the .opf file in Sigil, Sigil will under certain circumstances regenerate the .opf file. Did you by any chance manually edit the .opf file? If so what did you change?