Index: mercurial/context.py
===================================================================
--- mercurial/context.py
+++ mercurial/context.py
@@ -1980,6 +1980,8 @@
     def setbase(self, wrappedctx):
         self._wrappedctx = wrappedctx
         self._parents = [wrappedctx]
+        # Drop old manifest cache:
+        self._invalidate()
 
     def data(self, path):
         if self.isdirty(path):
@@ -1995,6 +1997,13 @@
         else:
             return self._wrappedctx[path].data()
 
+    def _invalidate(self):
+        # Unfortunately, this is necessary when rebasing several nodes with one
+        # ``overlayworkingctx`` (e.g. with --collapse); the manifest can change
+        # and make the cache outdated.
+        self._manifest = None
+        del self.__dict__["_manifest"]
+
     @propertycache
     def _manifest(self):
         parents = self.parents()