psnup and friends are always compiled to have a default output paper size of a4, this is set in the toplevel psutils Makefile. There should be a way for this default to be changed. Reproducible: Always
Ok, but how ? What I'd see would be a configuration file, which change should go upstream. In any case this only affects the default, you can still use non a4 paper, so its not a big issue. Closing as upstream for a feature request.