Index: branches/eam_branches/20090715/psModules/src/objects/pmSource.c
===================================================================
--- branches/eam_branches/20090715/psModules/src/objects/pmSource.c	(revision 25587)
+++ branches/eam_branches/20090715/psModules/src/objects/pmSource.c	(revision 25588)
@@ -933,4 +933,6 @@
     if (model == NULL) return false;  // model must be defined
 
+    bool addNoise = mode & PM_MODEL_OP_NOISE;
+
     if (source->modelFlux) {
         // add in the pixels from the modelFlux image
@@ -954,10 +956,9 @@
 
         psF32 **target = source->pixels->data.F32;
-        if (mode & PM_MODEL_OP_NOISE) {
-            // XXX need to scale by the gain...
+        if (addNoise) {
+	    // when adding noise, we assume the shape and Io have been modified
             target = source->variance->data.F32;
         }
 
-        // XXX need to respect the source and model masks?
         for (int iy = 0; iy < source->modelFlux->numRows; iy++) {
             int oy = iy + dY;
@@ -973,16 +974,27 @@
             }
         }
+	if (!addNoise) {
+	    if (add) {
+		source->tmpFlags &= ~PM_SOURCE_TMPF_SUBTRACTED;
+	    } else {
+		source->tmpFlags |= PM_SOURCE_TMPF_SUBTRACTED;
+	    }
+	}
         return true;
     }
 
     psImage *target = source->pixels;
-    if (mode & PM_MODEL_OP_NOISE) {
+    if (addNoise) {
         target = source->variance;
     }
 
-    if (add) {
-        status = pmModelAddWithOffset (target, source->maskObj, model, PM_MODEL_OP_FULL, maskVal, dx, dy);
-    } else {
-        status = pmModelSubWithOffset (target, source->maskObj, model, PM_MODEL_OP_FULL, maskVal, dx, dy);
+    if (!addNoise) {
+	if (add) {
+	    status = pmModelAddWithOffset (target, source->maskObj, model, PM_MODEL_OP_FULL, maskVal, dx, dy);
+	    source->tmpFlags &= ~PM_SOURCE_TMPF_SUBTRACTED;
+	} else {
+	    status = pmModelSubWithOffset (target, source->maskObj, model, PM_MODEL_OP_FULL, maskVal, dx, dy);
+	    source->tmpFlags |= PM_SOURCE_TMPF_SUBTRACTED;
+	}
     }