Index: openjpa-kernel/src/main/java/org/apache/openjpa/enhance/PCEnhancer.java
===================================================================
--- openjpa-kernel/src/main/java/org/apache/openjpa/enhance/PCEnhancer.java	(revision 509668)
+++ openjpa-kernel/src/main/java/org/apache/openjpa/enhance/PCEnhancer.java	(working copy)
@@ -95,6 +95,11 @@
  * @author Abe White
  */
 public class PCEnhancer {
+	// Designates a version for maintaining compatbility when PCEnhancer
+	// modifies enhancement that can break serialization or other contracts
+	// Each enhanced class will return the value of this field via
+	// public int getEnhancementContractVersion()
+    public static final int ENHANCER_VERSION = 2;
 
     public static final int ENHANCE_NONE = 0;
     public static final int ENHANCE_AWARE = 2 << 0;
@@ -716,7 +721,6 @@
         if (_meta.getPCSuperclass() == null) {
             addStockMethods();
             addGetVersionMethod();
-            addReplaceFlagsMethod();
             addReplaceStateManagerMethod();
 
             if (_meta.getIdentityType() != ClassMetaData.ID_APPLICATION)
@@ -841,11 +845,6 @@
         code.aload().setParam(0);
         code.putfield().setField(SM, SMTYPE);
 
-        // pc.pcFlags = LOAD_REQUIRED
-        code.aload().setLocal(inst);
-        code.constant().setValue(PersistenceCapable.LOAD_REQUIRED);
-        code.putfield().setField(PRE + "Flags", byte.class);
-
         // copy key fields from oid
         if (oid) {
             code.aload().setLocal(inst);
@@ -1330,35 +1329,6 @@
     }
 
     /**
-     * Adds the {@link PersistenceCapable#pcReplaceFlags}
-     * method to the bytecode.
-     */
-    private void addReplaceFlagsMethod() {
-        // public final void pcReplaceFlags ()
-        BCMethod method = _pc.declareMethod(PRE + "ReplaceFlags",
-            void.class, null);
-        Code code = method.getCode(true);
-
-        // if (pcStateManager != null)
-        loadManagedInstance(code, false);
-        code.getfield().setField(SM, SMTYPE);
-        JumpInstruction ifins = code.ifnonnull();
-        code.vreturn();
-
-        // pcFlags = pcStateManager.replaceFlags ();
-        ifins.setTarget(loadManagedInstance(code, false));
-        loadManagedInstance(code, false);
-        code.getfield().setField(SM, SMTYPE);
-        code.invokeinterface().setMethod(SMTYPE, "replaceFlags",
-            byte.class, null);
-        code.putfield().setField(PRE + "Flags", byte.class);
-        code.vreturn();
-
-        code.calculateMaxStack();
-        code.calculateMaxLocals();
-    }
-
-    /**
      * Adds the {@link PersistenceCapable#pcReplaceStateManager}
      * method to the bytecode.
      */
@@ -2157,6 +2127,9 @@
         // make the class implement PersistenceCapable
         _pc.declareInterface(PCTYPE);
 
+        // add a version stamp
+        addGetEnhancementContractVersionMethod();
+        
         // find the default constructor
         BCMethod method = _pc.getDeclaredMethod("<init>", (String[]) null);
 
@@ -2212,10 +2185,6 @@
             BCField field = _pc.declareField(SM, SMTYPE);
             field.makeProtected();
             field.setTransient(true);
-
-            field = _pc.declareField(PRE + "Flags", byte.class);
-            field.makeProtected();
-            field.setTransient(true);
         }
     }
 
@@ -2860,23 +2829,10 @@
             return;
         }
 
-        // dfg: if (inst.pcFlags <= 0) return inst.<field>;
-        JumpInstruction ifins = null;
-        if ((fieldFlag & PersistenceCapable.CHECK_READ) > 0) {
-            loadManagedInstance(code, true);
-            code.getfield().setField(PRE + "Flags", byte.class);
-            ifins = code.ifgt();
-            loadManagedInstance(code, true);
-            addGetManagedValueCode(code, fmd);
-            code.xreturn().setType(fmd.getDeclaredType());
-        }
-
         // if (inst.pcStateManager == null) return inst.<field>;
         Instruction ins = loadManagedInstance(code, true);
-        if (ifins != null)
-            ifins.setTarget(ins);
         code.getfield().setField(SM, SMTYPE);
-        ifins = code.ifnonnull();
+        JumpInstruction ifins = code.ifnonnull();
         loadManagedInstance(code, true);
         addGetManagedValueCode(code, fmd);
         code.xreturn().setType(fmd.getDeclaredType());
@@ -2919,25 +2875,10 @@
         // PCEnhancer uses static methods; PCSubclasser does not.
         int firstParamOffset = getAccessorParameterOffset();
 
-        // dfg: if (inst.pcFlags == 0) inst.<field> = value;
-        JumpInstruction ifins = null;
-        byte fieldFlag = getFieldFlag(fmd);
-        if ((fieldFlag & PersistenceCapable.CHECK_WRITE) > 0) {
-            loadManagedInstance(code, true);
-            code.getfield().setField(PRE + "Flags", byte.class);
-            ifins = code.ifne();
-            loadManagedInstance(code, true);
-            code.xload().setParam(firstParamOffset);
-            addSetManagedValueCode(code, fmd);
-            code.vreturn();
-        }
-
         // if (inst.pcStateManager == null) inst.<field> = value;
         Instruction ins = loadManagedInstance(code, true);
-        if (ifins != null)
-            ifins.setTarget(ins);
         code.getfield().setField(SM, SMTYPE);
-        ifins = code.ifnonnull();
+        JumpInstruction ifins = code.ifnonnull();
         loadManagedInstance(code, true);
         code.xload().setParam(firstParamOffset);
         addSetManagedValueCode(code, fmd);
@@ -3507,6 +3448,19 @@
         return setter;
     }
 
+    private void addGetEnhancementContractVersionMethod() {
+    	// public int getEnhancementContractVersion()
+    	BCMethod method = _pc.declareMethod("getEnhancementContractVersion", 
+    			int.class, null);
+    	method.makePublic();
+        Code code = method.getCode(true);
+        code.constant().setValue(ENHANCER_VERSION);
+        code.areturn();
+        code.calculateMaxStack();
+        code.calculateMaxLocals();
+        return;
+    }
+
     /**
      * Return the concrete type for the given class, i.e. impl for managed
      * interfaces