.opAssign disabled without @disable

[denizzzka via Digitalmars-d-learn]

On Sunday, 17 April 2016 at 06:42:39 UTC, denizzzka wrote:
> Tried to build small test app - is not reproduced.

Also tried to reduce source:
https://github.com/denizzzka/r-tree/tree/314f7f1cc1b6387915dc56dcb2d3ccbc63e19275/source

In this source line 199 causes this error
(https://github.com/denizzzka/r-tree/blob/314f7f1cc1b6387915dc56dcb2d3ccbc63e19275/source/package.d#L199)

But if I am checkout to master and remove const from
debug private const bool isLeafNode = false;

It isn't fixes compiling.

Second branch:
I am removed const from file and add import insted of traits 
template function:

https://github.com/denizzzka/r-tree/blob/4457025efa72a6d8a97429e09c35a3f5520c37d5/source/package.d#L26

If place this import to top of the file @disabled error is gone! 
Why?