Must a defendant continue to challenge a procedural bar ruling after being granted a Certificate of Appealability?

QUESTIONS PRESENTED ARE: 1. Must a defendant who has been granted a Certificate of Appealability by the Court of Appeals continue to challenge a procedural bar ruling by the district court on the issue after the Court of Appeals has issued a COA to appeal that issue or risk "abandonment" of the claim, or may the petitioner appeal the issue as described in the COA without further argument as to a procedural bar? 2. Where the government has engaged in pre-plea misconduct and misrepresentations, including but not limited to withholding and concealment of material exculpatory evidence, is a defendant who pleaded guilty while unaware of such evidence, precluded by circuit precedent based on Brady v. Maryland, from claiming that his plea was unknowing, unintelligent and involuntary under Brady v. United States?