First, thank you for your answer. Guess what, it works for me as well :(

The reason for my late answer is, that my problem is a bit more complex. I have a base class and create on the fly a Role and then a Class from that Role and the baseclass. Later I apply that role with the default/builder problem. Putting that together in my sample code works as well with builders.

Now I try to figure out where the difference is between my real code and the sample, as the real code still does give that error. (Not) Using MooseX::Declare does not make a difference.