When working with a document with 15 embedded graphics (namely EPS files), three
of the graphics got lost occasionally resulting in a Read Error.

Saving just after inserting is usually fine.  When I make a trivial change and
then save again, the pictures (SVM files) does not appear in the SXW file, and
the corresponding <draw:image ...> tag has no xlink:xxx attributes (these
attributes used to reference to the lost SVM files).  Then Read Errors will
sometimes appear (not always thanks to the graphics cache).  If I make another
trivial change and save again, the <draw:image...> tag disappears entirely, thus
there won't be any pictures or empty frames there at all if I close and reopen
the file.  I suppose such <draw:image ...> tags without xlink: attributes are
invalid.

The contents of my present file is private, but I will try my best to make a
test case upon request.  Anyway, test files probably won't be too useful since
everything relevent in them has been described above.  Just insert twenty or so
embedded EPS files into a document, save, change, save, change, save, and
observe the results.