Viktor, unfortunately Germany is a bit schizophrenic where its love-hate affair with the US is concerned. On the one hand they want to be their own nation, on the other they'll bend over backwards to assist the US with anything they get asked. The whole terrorist era in the seventies and eighties didn't help the paranoia much.
IST is Turkey, which is NOT an EU country or a Schengen signatory, so I wouldn't be surprised at a secondary check.
S.