You're right, it's because of namespace::autoclean
There is an example in the Moose Cookbook, of overloading with Moose : http://search.cpan.org/~stevan/Moose/lib/Moose/Cookbook/Basics/Recipe9.pod
It uses the overloading operator.
According to a namespace::autoclean review, if you use overloading with Moose you should use namespace::sweep instead of namespace::autoclean :
"This pragma was written to address some problems with the excellent namespace::autoclean. In particular, namespace::autoclean will remove special symbols that are installed by overload, so you can't use namespace::autoclean on objects that overload Perl operators."
