Using multiple mixin templates to implement operator overloading

[Tobias Pankrath via Digitalmars-d-learn]

I want to wrap e.g. an int and implement basic arithmetic. In the 
provided example [1] I use  two mixin templates to separately 
implement scaling (multiplication with int/double) and addition 
and subtraction with the type itself.

In the end I want to have several distinct wrappers and allow 
specific operations between them and int / double. It's important 
that the return values are typed correctly, otherwise I could use 
std.typecons.Proxy.

My problem is that both overloads of opBinary work, but not at 
the same time. As soon as I mixin both templates, they stop to 
work. If I just paste the implementation into the body of 
WrapInt, they work both at the same time though.

Could someone explain the mechanics behind it?

Thanks!

[1] https://run.dlang.io/is/WbG987