Originally Posted by TandemGeek

That looks to be Kent & Katie Eriksen's personal tandem. It was last year's NAHBS "Best Tandem". The shifting arrangement is very unique in that Katie has control over the shifting which can be configured with either a Di2 shifted front double or a mechanical front triple for touring in steep terrain. So, the thumb shifter does control the front derailleur, but there's also a Di2 remote shifter on the stoker's bars that can be used to control both the front & rear Di2 derailleurs. Katie also has control over the rear hydraulic disc drag brake.