do not violate the Ex Post Facto Clause. 5 . In his habeas petition, Bailey advanced several legal theories. One of them relied on the same Ex Post Facto Clause argument he advances here. The government asserts the present action is therefore barred on res judi-cata and collateral estoppel grounds. However, we need not decide this issue to resolve the case before us because neither collateral estoppel nor res judicata deprives the court of subject-matter jurisdiction. See Smalls v. United States, 471 F.3d 186, 189 (D.C.Cir.2006) ("[T]he defense of res judicata, or claim preclusion, while having a somewhat jurisdictional character, does not affect the subject matter jurisdiction of the district court.''): cf. Nat'l Treasury Emps. Union v. IRS, 765 F.2d 1174, 1176 n. 1 (D.C.Cir.1985) (<HOLDING>). ROGERS, Circuit Judge, concurring in part and
holding that laches is an affirmative defense holding that fair use is an affirmative defense holding that the time bar imposed by bankruptcy rule 4007c is an affirmative defense subject to waiver estoppel and equitable tolling recognizing that collateral estoppel or issue preclusion is an affirmative defense under fedrcivp 8c that is subject to waiver and forfeiture  and therefore holding implicitly that this defense is not an attack on the courts subjectmatter jurisdiction holding that the assertion that a plaintiff prisoner failed to exhaust all available administrative remedies as required under the plra is an affirmative defense under fedrcivp 8c it is the burden of the defendant asserting this affirmative de fense to plead and prove it