This issue can be resolved by making a change to the Riot compiler: Compile the whole of the tag constructor instead of just the constructor body. I submitted a pull request https://github.com/muut/riotjs/pull/280
My proposed solution is flawed so I closed the pull request. Irrespective of the resolution of the above `this` problem, if you use `--type=es6` then you cannot use the Riot "ES6-like" method syntax because it is not valid ES6 and throws 6to5 compile errors (the riot compiler only pre-processes ES6-like methods when `--type` is not explicitly specified). All in all, I'm not convinced `--type=es6` as a transpiler option is useful, you are better off using the default ES5 + "ES6-like" method syntax.
This issue is fixed with [this commit](https://github.com/muut/riotjs/commit/af32c6758b9f73a8f20e50ce3202f9d307b9545e)
Yes, seems fixed in 2.0.9.