Put back fix for SingleMode 3D output.

utilities/FieldConvert/Field.hpp

@@ -289,6 +289,16 @@ struct Field {
                         nplanes =  m_fielddef[0]->m_numModes[2];
                         lz      = m_fielddef[0]->m_homogeneousLengths[0];
                         btype   = m_fielddef[0]->m_basis[2];
+
+                        if (btype == LibUtilities::eFourierSingleMode)
+                        {
+                            btype = LibUtilities::eFourier;
+                            m_fielddef[0]->m_basis[2] = LibUtilities::eFourierSingleMode;
+                            if (nplanes <= 2)
+                            {
+                                nplanes = 4;
+                            }
+                        }
                     }
                     else
                     {