In the iOS app, I download three videos for offline use, listen to them in the car, come back home and download some more, rinse and repeat.
After doing this for a few days, I'll log in to the itpro.tv website on the PC, and none of my progress has been synced. It appears as though I have not watched any of the videos in that course.
Of course, if I stream videos in the iOS app while connected to wifi, my progress is properly synced when I log in on the PC :)
Only when downloading videos for offline use, watching the video offline, and then opening the app again later when connected to wifi to download some more, it appears that the progress made offline will not sync.