We seem to be deleting too many of the things

This clones the object from which we'd like to delete extra values so that when we delete them, they're not also killed from the place we'd like to use them. This problem doesn't express itself in the test suite, but seems to be occurring in production.

@harrietgrace - you have the full details on what we're debugging here, so if you've got a better approach here than my shooting in the dark, I'm all ears. Thanks!