Index: org/python/core/MergeState.java
===================================================================
--- org/python/core/MergeState.java	(revision 4523)
+++ org/python/core/MergeState.java	(working copy)
@@ -129,9 +129,10 @@
         pa = 0;
 
         this.data[dest++] = this.data[pb++];
-        --nb;
+        
         if (nb == 0)
             return;
+        --nb;
         if (na == 1) {
             // CopyB;
             System.arraycopy(this.data, pb, this.data, dest, nb);
@@ -254,9 +255,9 @@
         pa += na - 1;
 
         this.data[dest--] = this.data[pa--];
-        --na;
         if (na == 0)
             return;
+        --na;
         if (nb == 1) {
             // CopyA;
             dest -= na;