Index: trunk/psModules/src/objects/pmPCMdata.c
===================================================================
--- trunk/psModules/src/objects/pmPCMdata.c	(revision 31153)
+++ trunk/psModules/src/objects/pmPCMdata.c	(revision 31451)
@@ -263,8 +263,11 @@
 bool pmPCMupdate(pmPCMdata *pcm, pmSource *source, pmSourceFitOptions *fitOptions, pmModel *model) {
 
-    bool newWindow = (source->pixels->numRows != pcm->modelFlux->numRows) || (source->pixels->numCols != pcm->modelFlux->numCols);
+    bool sameWindow = (source->pixels->numRows == pcm->modelFlux->numRows);
+    sameWindow     &= (source->pixels->numCols == pcm->modelFlux->numCols);
+    sameWindow     &= (source->pixels->col0    == pcm->modelFlux->col0);
+    sameWindow     &= (source->pixels->row0    == pcm->modelFlux->row0);
 
     // re-count the number of unmasked pixels:
-    if (newWindow) {
+    if (!sameWindow) {
 	for (psS32 i = 0; i < source->pixels->numRows; i++) {
 	    for (psS32 j = 0; j < source->pixels->numCols; j++) {
@@ -346,5 +349,5 @@
 
     // has the source pixel window changed?
-    if (newWindow) {
+    if (!sameWindow) {
 
 	// adjust all supporting images: