AssertionError when building element with workspace after clearing cache

After deleting my ~/.cache/buildstream, I hit this assertion error when building glib-networking (for which I have an open workspace). BuildStream should be robust to this situation:

[00:00:02][????????][build:core/glib-networking.bst      ] BUG     Build

    An unhandled exception occured:
    
    Traceback (most recent call last):
      File "/home/mcatanzaro/.local/lib/python3.6/site-packages/buildstream/_scheduler/job.py", line 320, in _child_action
        result = self._action_cb(element)
      File "/home/mcatanzaro/.local/lib/python3.6/site-packages/buildstream/_scheduler/buildqueue.py", line 34, in process
        element._assemble()
      File "/home/mcatanzaro/.local/lib/python3.6/site-packages/buildstream/element.py", line 1409, in _assemble
        self.stage(sandbox)
      File "/home/mcatanzaro/.local/lib/python3.6/site-packages/buildstream/buildelement.py", line 165, in stage
        self.stage_dependency_artifacts(sandbox, Scope.BUILD)
      File "/home/mcatanzaro/.local/lib/python3.6/site-packages/buildstream/element.py", line 666, in stage_dependency_artifacts
        old_dep_keys = self.__get_artifact_metadata_dependencies(workspace.last_successful)
      File "/home/mcatanzaro/.local/lib/python3.6/site-packages/buildstream/element.py", line 2350, in __get_artifact_metadata_dependencies
        artifact_base, key = self.__extract(key)
      File "/home/mcatanzaro/.local/lib/python3.6/site-packages/buildstream/element.py", line 2302, in __extract
        return (self.__artifacts.extract(self, key), key)
      File "/home/mcatanzaro/.local/lib/python3.6/site-packages/buildstream/_artifactcache/ostreecache.py", line 105, in extract
        assert rev, "Artifact missing for {}".format(ref)
    AssertionError: Artifact missing for gnome/core-glib-networking/851a17f63e24689c382960ffd56c3efb872e7e97c6533836bd5d4abbe02aba40