Index: branches/simmosaic_branches/psphot/src/psphotImageLoop.c
===================================================================
--- branches/simmosaic_branches/psphot/src/psphotImageLoop.c	(revision 24860)
+++ branches/simmosaic_branches/psphot/src/psphotImageLoop.c	(revision 27839)
@@ -67,18 +67,19 @@
 
                 // Update the header
-                {
-                    pmHDU *hdu = pmHDUGetHighest(input->fpa, chip, cell);
-                    if (hdu && hdu != lastHDU) {
-                        psphotVersionHeaderFull(hdu->header);
-                        lastHDU = hdu;
-                    }
+		pmHDU *hdu = pmHDUGetHighest(input->fpa, chip, cell);
+		if (hdu && hdu != lastHDU) {
+		    psphotVersionHeaderFull(hdu->header);
+		    lastHDU = hdu;
                 }
 
-                psImageMaskType maskSat = pmConfigMaskGet("SAT", config); // Mask value for saturated pixels
-                if (!pmReadoutMaskNonfinite(readout, maskSat)) {
-                    psError(psErrorCodeLast(), false, "Unable to mask non-finite pixels.");
-                    psFree(view);
-                    return false;
-                }
+		// if an external mask is supplied, ensure that NAN pixels are also masked
+		if (readout->mask) {
+		    psImageMaskType maskSat = pmConfigMaskGet("SAT", config); // Mask value for saturated pixels
+		    if (!pmReadoutMaskNonfinite(readout, maskSat)) {
+			psError(psErrorCodeLast(), false, "Unable to mask non-finite pixels.");
+			psFree(view);
+			return false;
+		    }
+		}
 
                 // run the actual photometry analysis on this chip/cell/readout
@@ -90,15 +91,15 @@
             }
 
-            status = true;
-            status &= pmFPAfileDropInternal (config->files, "PSPHOT.BACKMDL");
-            status &= pmFPAfileDropInternal (config->files, "PSPHOT.BACKMDL.STDEV");
-            status &= pmFPAfileDropInternal (config->files, "PSPHOT.BACKGND");
-            if (!status) {
-                psError(PSPHOT_ERR_PROG, false, "trouble dropping internal files");
-                psFree (view);
-                return false;
-            }
+	    // drop all versions of the internal files
+	    status = true;
+	    status &= pmFPAfileDropInternal (config->files, "PSPHOT.BACKMDL");
+	    status &= pmFPAfileDropInternal (config->files, "PSPHOT.BACKMDL.STDEV");
+	    status &= pmFPAfileDropInternal (config->files, "PSPHOT.BACKGND");
+	    if (!status) {
+		psError(PSPHOT_ERR_PROG, false, "trouble dropping internal files");
+		psFree (view);
+		return false;
+	    }
         }
-
         // save output which is saved at the chip level
         if (!pmFPAfileIOChecks (config, view, PM_FPA_AFTER)) ESCAPE ("failed output for Chip in psphot.");