Index: branches/tap_branches/ppSub/src/ppSubDefineOutput.c
===================================================================
--- branches/tap_branches/ppSub/src/ppSubDefineOutput.c	(revision 25900)
+++ branches/tap_branches/ppSub/src/ppSubDefineOutput.c	(revision 27838)
@@ -51,17 +51,20 @@
     bool mdok;                          // Status of MD lookup
     psMetadata *analysis = inConv->analysis; // Analysis metadata with kernel information
-    pmSubtractionKernels *kernels = psMetadataLookupPtr(&mdok, analysis,
-                                                        PM_SUBTRACTION_ANALYSIS_KERNEL); // Subtraction kernel
+    pmHDU *hdu = pmHDUFromCell(inConv->parent);
+    pmSubtractionKernels *kernels = psMetadataLookupPtr(&mdok, analysis, PM_SUBTRACTION_ANALYSIS_KERNEL); // Subtraction kernel
+
     if (!kernels) {
+        hdu = pmHDUFromCell(refConv->parent);
         analysis = refConv->analysis;
         kernels = psMetadataLookupPtr(&mdok, analysis, PM_SUBTRACTION_ANALYSIS_KERNEL);
     }
     if (!kernels) {
-        psError(PS_ERR_UNEXPECTED_NULL, true, "Unable to find SUBTRACTION.KERNEL");
+        psError(PPSUB_ERR_UNKNOWN, true, "Unable to find SUBTRACTION.KERNEL");
         psFree(outRO);
         return false;
     }
-    psMetadataAddStr(outHDU->header, PS_LIST_TAIL, "PPSUB.KERNEL", 0, "Subtraction kernel",
-                     kernels->description);
+    psAssert (hdu, "unable to find HDU");
+    psMetadataAddStr(outHDU->header, PS_LIST_TAIL, "PPSUB.KERNEL", 0, "Subtraction kernel", kernels->description);
+    outHDU->header = psMetadataCopy(outHDU->header, hdu->header);
 
     // Add additional data to the header