Clear siblings, now that they are being set.
diff --git a/Lib/xml/dom/minidom.py b/Lib/xml/dom/minidom.py
index 6dc3a52..00bd4ca 100644
--- a/Lib/xml/dom/minidom.py
+++ b/Lib/xml/dom/minidom.py
@@ -136,6 +136,8 @@
             self.childNodes[-1].unlink()
             del self.childNodes[-1] # probably not most efficient!
         self.childNodes = None
+        self.previousSibling = None
+        self.nextSibling = None
         if self.attributes:
             for attr in self._attrs.values():
                 self.removeAttributeNode(attr)