"Frankie Drake Mysteries" not the same as "Finding Your Roots"

This evening I selected 42.1 from the program guide to watch the Frankie Drake Mysteries (WXEL, PBS) only to find myself watching Finding Your Roots from a different PBS station!

I suspect that 42.1 was too weak a signal to be pulled in and Channels DVR thought that Finding Your Roots would be a good substitute! One word WRONG!

How do I turn this insane "feature" off? I would rather be told "weak signal" instead.