Index: trunk/psModules/src/camera/pmHDU.c
===================================================================
--- trunk/psModules/src/camera/pmHDU.c	(revision 24298)
+++ trunk/psModules/src/camera/pmHDU.c	(revision 24312)
@@ -93,12 +93,31 @@
     }
 
+    psTrace("psModules.camera", 5, "Reading the header...\n");
+
+    // The header may already exist (e.g., from doing concept writing at the PHU level) so we need to be
+    // careful.  We read into a separate container and copy that over the top of anything that's already read.
+    psMetadata *header = psFitsReadHeader(NULL, fits);
+    if (!header) {
+        psError(PS_ERR_IO, false, "Unable to read header for extension %s\n", hdu->extname);
+        return false;
+    }
+
     if (!hdu->header) {
-        psTrace("psModules.camera", 5, "Reading the header...\n");
-        hdu->header = psFitsReadHeader(hdu->header, fits);
-        if (! hdu->header) {
-            psError(PS_ERR_IO, false, "Unable to read header for extension %s\n", hdu->extname);
-            return false;
-        }
-    }
+        hdu->header = header;
+        return true;
+    }
+
+    psMetadataIterator *iter = psMetadataIteratorAlloc(header, PS_LIST_HEAD, NULL); // Iterator
+    psMetadataItem *item;           // Item from iteration
+    while ((item = psMetadataGetAndIncrement(iter))) {
+        const char *name = item->name; // Name of item
+        if (psMetadataLookup(hdu->header, name)) {
+            // It exists; clobber
+            psMetadataRemoveKey(hdu->header, name);
+        }
+        psMetadataAddItem(hdu->header, item, PS_LIST_TAIL, 0);
+    }
+    psFree(iter);
+    psFree(header);
 
     return true;