On_cancel not working with slack notifications

Setting on_cancel to never for slack notifications still sends a slack notification. The rest of the configurations are behaving correctly.

My configuration -

      - secure: hidden
    on_pull_requests: false
    on_success: never
    on_failure: always
    on_error: always
    on_cancel: never

I initially reached out to the slack team and they directed me here
From Slack -
“After viewing the logs, I can confirm that we are still receiving the “canceled” events from Travis CI, so the event filtering is not happening within their product.”

Thanks for the help!