About cuando - the "lesson"is confusing at best

Question

The difference between an "event still to happen" and one that "will happen" can be determined only by the ability to predict the future. It is not a grammatical issue. So neither the indicative nor subjunctive choice is grammatically incorrect. It's a semantic difference, not a grammatical one. I've seen you make very different choices -- different from what I thought was meant.

Answer

Hola Marc
I'm not sure that you understood correctly when reading the lesson.
The difference between using the indicative and using the subjunctive with cuando is 1. talking about a habitual event, i.e. something that actually happens, as in "everytime I....", and 2. talking about a future event. 
You can also see by reading what the main clause says if that is something that is a habitual event or something still to happen. For example, using the future tense or the imperative in the main clause indicates a still to happen action in the cuando clause:
Visitaré a mi abuela cuando vaya a Málaga.
Visita el Museo del Prado cuando vayas a Madrid.
All these are still to happen.
However:
Yo visito a mi abuela cuando voy a Málaga.
This is a habitual event (I visit my grandma every time I go to Málaga) 
Saludos cordiales
Inma