Prosecutorial Immunity for Civil Habeas Proceeding?

Isn't a habeas proceeding a collateral proceeding?  It's a civil proceeding, right?  We hear this all of the time.  A habeas petitioner doesn't have the full rights we learned about in Criminal Procedure because a habeas proceeding is not a criminal proceeding.  Simple enough, right?

That simple distinction changes when a criminal prosecutor has withheld exculpatory evidence in a civil proceeding.  Suddenly the prosecutor is acting as a prosecutor - even though it's a civil proceeding.  This is all nonsense, of course, that is designed to protect prosecutors who commit violations of the Constitution and Rules of Professional Conduct.

See this report on Warney v. Monroe County, 08-0947 (2d Cir. Nov. 13, 2009) (here).