There is a bug when you are using 2 synced sliders on a touch device (mobile); if you swipe the main slider to go to the next slide, the sync'ed nav slider will also transform and display the appropriate "active" slide; however, when you swipe back (to go back to the first slide), the nav slider will properly set the active slide however it will not transform back to its default state (translate3d(0px, 0px. 0px)) so therefore the user can no longer visually see the first slide in the nav slider at all. This only seems to happen when going back to the first slide (ie. if you swipe and to forward 3-4 slides, you can swipe back and it will work as expected until you are trying to swipe back to the first slide)
My implementation is not public; however, you can see this bug on the main flexslider demo for the carousel version on woothemes (http://flexslider.woothemes.com/thumbnail-slider.html); just make sure you do it in emulated mobile mode.
There is a bug when you are using 2 synced sliders on a touch device (mobile); if you swipe the main slider to go to the next slide, the sync'ed nav slider will also transform and display the appropriate "active" slide; however, when you swipe back (to go back to the first slide), the nav slider will properly set the active slide however it will not transform back to its default state (translate3d(0px, 0px. 0px)) so therefore the user can no longer visually see the first slide in the nav slider at all. This only seems to happen when going back to the first slide (ie. if you swipe and to forward 3-4 slides, you can swipe back and it will work as expected until you are trying to swipe back to the first slide)
My implementation is not public; however, you can see this bug on the main flexslider demo for the carousel version on woothemes (http://flexslider.woothemes.com/thumbnail-slider.html); just make sure you do it in emulated mobile mode.