In a rush, I’d called my migration “vendorServiceKEy”
Which had resulted in my migration being named 201512102031458_vendorServiceKEy
I then ran migrations with update-database.
Now, when I renamed the class manually, to sort out my OCD, the next time my application ran, I got
There is already an object named xxx in the database
My _MigrationHistory table contained the following entry:
Renaming this to the correctly camel-cased version allowed EF to know this migration (although renamed) had already been run, and to ignore it