What's the deal with "Warning: explicit element-wise assignment..."

[monarch_dodra via Digitalmars-d]

On Tuesday, 15 April 2014 at 06:31:02 UTC, Andrei Alexandrescu 
wrote:
> We've just enabled warnings as errors in our build system at 
> work and suddenly:
>
> Warning: explicit element-wise assignment <exprnew> is better 
> than <expr>
>
> where <exprnew> and <expr> are expressions picked from the 
> code. For example, this wasn't accepted:
>
> writeAvail_[0 .. buf.length] = buf;
>
> but this was:
>
> writeAvail_[0 .. buf.length] = buf[];
>
> The type of the involved variables were as trivial as ubyte[] 
> and in ubyte[] respectively.
>
> What's the idea?
>
>
> Andrei

Funny, I can reproduce up to 2.063.2, but not after that.