diff --git a/IPython/core/interactiveshell.py b/IPython/core/interactiveshell.py
index 56aea6d..cbe3233 100644
--- a/IPython/core/interactiveshell.py
+++ b/IPython/core/interactiveshell.py
@@ -874,6 +874,8 @@ class InteractiveShell(SingletonConfigurable):
     def init_events(self):
         self.events = EventManager(self, available_events)
 
+        self.events.register("pre_execute", self._clear_warning_registry)
+
     def register_post_execute(self, func):
         """DEPRECATED: Use ip.events.register('post_run_cell', func)
         
@@ -883,6 +885,13 @@ class InteractiveShell(SingletonConfigurable):
              "ip.events.register('post_run_cell', func) instead.")
         self.events.register('post_run_cell', func)
     
+    def _clear_warning_registry(self):
+        # clear the warning registry, so that different code blocks with
+        # overlapping line number ranges don't cause spurious suppression of
+        # warnings (see gh-6611 for details)
+        if "__warningregistry__" in self.user_global_ns:
+            del self.user_global_ns["__warningregistry__"]
+
     #-------------------------------------------------------------------------
     # Things related to the "main" module
     #-------------------------------------------------------------------------
diff --git a/IPython/core/tests/test_interactiveshell.py b/IPython/core/tests/test_interactiveshell.py
index b9e76c2..1e8bfae 100644
--- a/IPython/core/tests/test_interactiveshell.py
+++ b/IPython/core/tests/test_interactiveshell.py
@@ -843,3 +843,17 @@ class TestSyntaxErrorTransformer(unittest.TestCase):
 
 
 
+def test_warning_suppression():
+    ip.run_cell("import warnings")
+    try:
+        with tt.AssertPrints("UserWarning: asdf", channel="stderr"):
+            ip.run_cell("warnings.warn('asdf')")
+        # Here's the real test -- if we run that again, we should get the
+        # warning again. Traditionally, each warning was only issued once per
+        # IPython session (approximately), even if the user typed in new and
+        # different code that should have also triggered the warning, leading
+        # to much confusion.
+        with tt.AssertPrints("UserWarning: asdf", channel="stderr"):
+            ip.run_cell("warnings.warn('asdf')")
+    finally:
+        ip.run_cell("del warnings")