This started happening either with my upgrade to iOS6 on my iPhone 4, or with my iPhone 5. I don't remember which.
1. Have a series recording for a series I lost interest in (in my case, Vegas).
2. Open the iPhone app. Wait; let it populate the guide.
3. Press My Week.
4. Find Vegas. Tap it. Tap Remove Series from recorder.
5. App crashes back to the home screen.
I think it also happens if I just do a Remove Episode.
Other actions like adding new recordings are unaffected.
Edit: I raised a proper support ticket (#19910) for this.