Hi @sjporter -
Thanks for the detailed bug report! This issue has come up in another context recently with the Java Snippet node too (Endlessly running JavaSnippets can't be canceled), and we recently created a ticket around that (Internal: AP-14266). I will add a link to your comments to that ticket as a +1.
Sorry for the annoyance with having to manually shutdown. I hope we’ll be able to knock this one out soon.