Recipe: Starting with the attached file:
  Open it with gnumeric.  Observe two plots.
   -- One has truly a single point.
   -- The other has a range that could cover two points,
     although the second point is has non-numerical data
     so it doesn't get plotted.
  $x/ssconvert singleton.gnumeric singleton.ods
    -- No errors or warnings.
  Open the .ods file.  
  Observe pop-up warning:  
     "Not enough data in the supplied range ((null)) for all the requests"
  Dismiss the popup.  Observe that the singleton point has vanished.
  The range-based point remains fine.
  Recreate the lost point.  It "looks" fine on the screen, so the
   obvious first guess is that the problem is in the i/o section,
   not the basic charting section.
  Save, exit, reopen the file.
  Same warning, same point lost again.
  Re-create the point again.
  Save As "foo.gnumeric".  Quit.
  Open foo.gnumeric.  Observe everything is OK.

Related:
  $x/ssconvert singleton.ods bar.gnumeric
does *not* produce a popup or any other error message, but
still the singleton point gets trashed.

This is not urgent for me, because there is a workaround,
but it sure did cause people to waste a bunch of time.


$x/ssconvert --version
ssconvert version '1.12.20'
datadir := '/usr/src/gnumeric/gitball/gnumeric/1.12.20'
libdir := '/usr/src/gnumeric/gitball/'


uname -a
Linux asclepias 3.18.0+ #2 SMP Sun Dec 21 18:25:03 MST 2014 x86_64 x86_64 x86_64 GNU/Linux