I upgraded to the newest plantuml.jar and had to add a "skin rose" to all my plantuml source files to keep the former standard skin (which IMHO looks much better than the actual default theme ;-)) for UML class diagrams.
When I than try to overwrite a skin parameter on the command line with e.g. -SclassFontName=Arial the complete skin is switched back to the new default theme and the rose skin settings seem to be ignored. I think this isn't intended.