It looks like this may be configured in the Recurrence part of the Pattern Task input variable. I've personally not used this component, so I can't say for sure. Looks like if you elect to "Remove Recurrence" in the configuration, it deletes all occurrences, whereas if you target a specific occurrence it will delete the one. Again, just guessing, as no other replies have come in yet.
I'm glad to have a look at your live problem if you'd like.