I don't get it. Strangest thing I've ever seen.
It can't be vandalism, because a) there are no impact spots and both are cracked in the same manner (3 cracks at the washer). Could this be it? Too much strain from the headlight washer over time ?

Really strange, you theory about the headlight washers sounds possible to me.

The more I look at the headlights, the more it bothers me I can't figure out what kind of car it is

Opel Astra H

i like that car...especially the wheels lol.
anyways, sucks about the light. is it getting hot there? does glass expand in heat? there's moisture...weather change perhaps.

I'm pretty sure it's plastic, most are.

Maybe the washer fluid is too strong. I know some of the fittings in my washer fluid lines will wear away over time it too strong a solution is used.

Another theory is : I run around all day with my lights on (it's the law) and the headlight washer comes on at the same time with the windshield wipers. Do that 5-6 times a day, 2 years straight and the casing will crack from the thermal shock (heat from the sun + lights vs. coolness form the washer fluid).

Its possible, but your washer solvent absorbs the heat of the engine bay as your driving. When its sprayed, its pretty warm, although with the alcohol content it flash evaporates very quickly and could cause the cracking. The only reason why i dont think that this is the cause though is there are many plastic lensed headlights with washers on them that dont show this kind of behavior.

Is the car under a factory warranty? If so, the fact that there is no impact damage, and both headlights exhibit the same fracture could easily get them replaced.

I plan to do that first thing monday morning.

My brother also has an Astra H. And he had the same problem!!!

The local dealer got the go ahead from Opel Romania to do the work under warranty. I'm expecting the new lights later this week.