>Do you have a citation for those cases? I’m not doubting you, but the legal sophistry to argue that an ex post facto law was constitutional despite the explicit prohibition would be >interesting. I’ve heard of cases where higher penalties were applied than existed at the time (which IIRC is banned by the ECHR and possibly the CCPR, although is allowed in the USA >and elsewhere), or where statutes of limitations were extended, but a blatant ex post facto law seems surprising.

Yes, I too haven't seen any ex post facto law; however, as I recall ex post facto prohibition only works on criminal cases, not civil. 
I saw an indication of a criminal case where the limitations period was illegally extended.   http://www.crimemagazine.com/firefighter-case-part-i      I met two of these convicts while in prison, and I am absolutely convinced that they were falsely convicted.  Worst, they were charged about 10 years after the crime, when the statute of limitations was about 5 years.  There was no limitations period for crimes punishable by death, but the crime occurred during a time in which the Feds did not have a death penalty.  Thus, the appeals court simply and deliberately violated the law.   http://crimemagazine.com/analysis-8th-circuit-opinion-firefighters-case    (However, on a skim I don't see reference to the statute of limitations issue here.)
         Jim Bell