Wouldn't the Frankfurt ruling conflict with the ruling from the ECJ? So, wouldn't overtime have to be explicitly mentioned as a mandatory component in the contract? Of course, it's only an ECJ ruling, so it's not binding until a corresponding national law exists. But somehow it seems to have already found its way in, if you look at the many references to this topic on Google.
And this also doesn't align with the ruling from Frankfurt. Or perhaps the Süddeutsche has omitted an important detail - because transferring files doesn't sound like an emergency or an extraordinary operational situation to me. And also that the employee would have had an explicit notice about the overtime obligation.
Of course, I'm not a lawyer and therefore probably not suited to follow the strange thought processes of judges and lawyers, but somehow it's been on my mind what the ARD guide says - and that's pretty much the opposite of what the ruling in Frankfurt says according to the Süddeutsche ...