diff --git a/runtime-testsuite/test/org/antlr/v4/test/runtime/descriptors/ParseTreesDescriptors.java b/runtime-testsuite/test/org/antlr/v4/test/runtime/descriptors/ParseTreesDescriptors.java
index ea3374f63..6db9769e8 100644
--- a/runtime-testsuite/test/org/antlr/v4/test/runtime/descriptors/ParseTreesDescriptors.java
+++ b/runtime-testsuite/test/org/antlr/v4/test/runtime/descriptors/ParseTreesDescriptors.java
@@ -112,7 +112,7 @@ public class ParseTreesDescriptors {
 
 		@Override
 		public boolean ignore(String targetName) {
-			return !targetName.equals("Java");
+			return !targetName.matches("Java|Python2|Python3");
 		}
 	}
 
diff --git a/runtime/Python2/src/antlr4/ParserRuleContext.py b/runtime/Python2/src/antlr4/ParserRuleContext.py
index f0eb4995f..8f68b2ef1 100644
--- a/runtime/Python2/src/antlr4/ParserRuleContext.py
+++ b/runtime/Python2/src/antlr4/ParserRuleContext.py
@@ -46,6 +46,15 @@ class ParserRuleContext(RuleContext):
         self.exception = None
 
     #* COPY a ctx (I'm deliberately not using copy constructor)#/
+    #
+    # This is used in the generated parser code to flip a generic XContext
+    # node for rule X to a YContext for alt label Y. In that sense, it is
+    # not really a generic copy function.
+    #
+    # If we do an error sync() at start of a rule, we might add error nodes
+    # to the generic XContext so this function must copy those nodes to
+    # the YContext as well else they are lost!
+    #/
     def copyFrom(self, ctx):
         # from RuleContext
         self.parentCtx = ctx.parentCtx
@@ -54,6 +63,15 @@ class ParserRuleContext(RuleContext):
         self.start = ctx.start
         self.stop = ctx.stop
 
+        # copy any error nodes to alt label node
+        if ctx.children is not None:
+            self.children = []
+            # reset parent pointer for any error nodes
+            for child in ctx.children:
+                if isinstance(child, ErrorNodeImpl):
+                    self.children.append(child)
+                    child.parentCtx = self
+
     # Double dispatch methods for listeners
     def enterRule(self, listener):
         pass
diff --git a/runtime/Python3/src/antlr4/ParserRuleContext.py b/runtime/Python3/src/antlr4/ParserRuleContext.py
index e72c6e04f..7ac4a750e 100644
--- a/runtime/Python3/src/antlr4/ParserRuleContext.py
+++ b/runtime/Python3/src/antlr4/ParserRuleContext.py
@@ -51,6 +51,15 @@ class ParserRuleContext(RuleContext):
         self.exception = None
 
     #* COPY a ctx (I'm deliberately not using copy constructor)#/
+    #
+    # This is used in the generated parser code to flip a generic XContext
+    # node for rule X to a YContext for alt label Y. In that sense, it is
+    # not really a generic copy function.
+    #
+    # If we do an error sync() at start of a rule, we might add error nodes
+    # to the generic XContext so this function must copy those nodes to
+    # the YContext as well else they are lost!
+    #/
     def copyFrom(self, ctx:ParserRuleContext):
         # from RuleContext
         self.parentCtx = ctx.parentCtx
@@ -59,6 +68,15 @@ class ParserRuleContext(RuleContext):
         self.start = ctx.start
         self.stop = ctx.stop
 
+        # copy any error nodes to alt label node
+        if ctx.children is not None:
+            self.children = []
+            # reset parent pointer for any error nodes
+            for child in ctx.children:
+                if isinstance(child, ErrorNodeImpl):
+                    self.children.append(child)
+                    child.parentCtx = self
+
     # Double dispatch methods for listeners
     def enterRule(self, listener:ParseTreeListener):
         pass