Assigning to class struct member leading to unexpected behavior.

[Paul via Digitalmars-d-learn]

I'm experiencing a compile error, but for the life of me, I 
cannot figure out what is wrong.

I'll try to keep it short but the code is roughly as follows:
class Window{
   Screen screen;
   alias screen this;
    this() {
        Screen s = {bottom_f: {[0, 1]}};
        this.screen = s; // Works
        this.screen = {bottom_f: {[0, 1]}}; // Leads to the 
list of errors below
    }
    ...
}

struct Screen{
    Vec!(2, int) bottom_f;
    ...
}

alias Vec(uint size, Type) = Mat!(size, 1, Type);

struct Mat(uint rows, uint columns = rows, Type = float) {
    private enum uint size = rows * columns;
    union{
        Type[columns][rows] mat;
        Type[size] vec;
    }
    static if (columns == 1) alias vec this;
    else alias mat this;
    . . .
}


List of errors:
1. "Label "bottom_f" is not used."
2. "expected ; instead of }"
3. "found `}` when expecting `;` following statement"
4. "use `{ }` for an empty statement, not `;`"
5. "found `void` when expecting `;` following statement" (later 
at function below constructor)

Why would assigning to a member variable lead to errors when 
using an intermediate variable of the same type does not?
I tried tweaking a lot but I just can't figure it out. Am I doing 
something wrong?