Under Nebraska law applicable at the time of the defendant's crime, one spouse could not testify against the other. After the defendant's second conviction was reversed on appeal, Nebraska changed its law so that a spouse could be compelled to testify where the crime involved violence. The Eighth Circuit held that this change in the rules of evidence was not an ex post facto violation. Palmer v. Clarke, No. 03-3841, slip op. at 7-11 (8th Cir. May 13, 2005).
Arguably, the holding would be dicta in federal cases, since the court conducted AEDPA review. But the panel seemed certain that even absent the AEDPA, such a change in the rules of evidence would never violate the Ex Post Facto Clause.
There was also an interesting bill of attainder issue, which I discussed here.