Originally Posted by
caspritz78
It should not. Cologne is a through train station. Does your train stop at Frankfurt central station? If yes, it will change directions there because Frankfurt central station is a terminus.
It seems that all the Duisburg - Stuttgart direct ICEs (which in fact run Dortmund - Duisburg - Stuttgart - Munich) go via Frankfurt Flughafen (which is also a through station), not Frankfurt Hbf.
Although Cologne is a through station, I thought a few trains reversed there - but I might be entirely wrong. However, the Duisburg - Stuttgart ICEs only have a 6 minute stop there, and I think DB schedules generally allow a bit longer than that, if a train is reversing.