System.InvalidOperationException: Correlation value specified does not match the already initialized correlation value on declaration approveRejectTas

Continuing with new discoveries of SharePoint workflow stuff, I ran into this logged exception after I added a SendEmail activity to my previously working workflow. So I know it's gotta be something in this Activity, which runs after a new Task is created in the workflow. Like every other Activity in the pipeline of the task process (Create Task, OnTaskChanged, CompleteTask etc), I gave this one the same correlation token as the task level token. Turn out that's the problem. Apparently the SendEmail activity (and a few other activities such as LogActivity) can only assume the workflow level correlation token.