Consideration of whether enforcing an appellate waiver in a plea deal would be a miscarriage of justice refers to the harm alleged in the appeal, not whether the mechanics of the plea deal itself work a miscarriage of justice.
http://media.ca1.uscourts.gov/pdf.opinions/15-1981P-01A.pdf
Since 2011. An occasional commonplacing of the U.S. Circuit Courts of Appeal.
Neither an authoritative statement of the law nor legal advice. Quick work.