Created attachment 223942 [details]
the missing sample

We seem to save the conditional style:
      <style:map style:apply-style-name="Gnumeric-1" style:condition="of:cell-content()=1" style:base-cell-address="$'Feuille1'.$A$1"/>

correctly referring to:
    <style:style style:name="Gnumeric-1" style:family="table-cell" style:data-style-name="ND.0">
      <style:table-cell-properties style:print-content="true" style:decimal-places="13" style:repeat-content="false"/>
      <style:paragraph-properties/>
      <style:text-properties/>
    </style:style>

but we are missing the data style ND.0!

It looks like we are using any data style that is only used within  a conditional style. The reason for this is that we write the conditional styles after we have already written the data styles:

odf_write_office_styles (GnmOOExport *state)
{
	gsf_xml_out_start_element (state->xml, OFFICE "styles");

	g_hash_table_foreach (state->xl_styles, (GHFunc) odf_write_this_xl_style, state);
	g_hash_table_foreach (state->xl_styles_neg, (GHFunc) odf_write_this_xl_style_neg, state);
	g_hash_table_foreach (state->xl_styles_zero, (GHFunc) odf_write_this_xl_style_zero, state);
	g_hash_table_foreach (state->xl_styles_conditional, (GHFunc) odf_write_this_conditional_xl_style, state);

	g_hash_table_foreach (state->named_cell_style_regions, (GHFunc) odf_save_this_style_with_name, state);
...

This problem has been fixed in the development version. The fix will be available in the next major software release. Thank you for your bug report.

To be specific: the data formats are now saved. For the file attached to this bug no change is visible because of bug # 683801. We do not save the custom format "" correctly. This is unrelated to the use of conditional formats.