The documentation for BasicEntityVisitor shows a Visit overload for DxfMLeader, but the visibility of the method is wrong and you can't override it in a derived class. I worked around this by implementing IEntityVisitor.Visit(DxfMLeader leader) explicitly in my class.

You're right, 2 methods were not virtual indeed, I've just fixed it. Please download the latest CadLib 4.0 version. Thank you for the report! - Wout

Thanks for the quick fix.