Index: trunk/psModules/src/imcombine/pmSubtraction.c
===================================================================
--- trunk/psModules/src/imcombine/pmSubtraction.c	(revision 20568)
+++ trunk/psModules/src/imcombine/pmSubtraction.c	(revision 20832)
@@ -1238,5 +1238,5 @@
     // and everything is executing psThreadPoolWait, waiting for some other mythical thread to complete the
     // thread's work.
-    psImageConvolveSetThreads(false);
+    bool oldThreads = psImageConvolveSetThreads(false); // Old value of threading for psImageConvolve
 
     if (stride == 0) {
@@ -1333,4 +1333,6 @@
     }
 
+    psImageConvolveSetThreads(oldThreads);
+
     psFree(sys1);
     psFree(sys2);