This is a ridiculous situation. A flyer reading the Schengen visa rules, and applying correctly according to his itenary, will be at high risk of losing both the money spent on his TK ticket, as well as suffering other costs and inconveniences, because TK itself does not follow the
Schengen visa rules.

I don't see any reason why a traveler should expect that this is something he needs to be wary of in any way. I would love to see someone sue TK for the misery and cost they are undoubtedly causing a lot of people who are doing everything correctly.