I'd recommend you avoid using Safe. It's going to break things frequently. I also recommend you avoid using Data::Dumper for persistence. It's great for debugging, but Storable is much better for persistence, and CGI::Session supports it.
Comment on Re: CGI::Session cannot read data from Data::Dumper
Thanks, it seems that it will do the trick for what I need.
However, this question remains: why $mdr, which is a Md object, cannot execute the param() method?