My family just got back from a three week trip around Germany, and we got jacked by DBahn, twice! The first time was in Dresden. We purchased a Dresen Regional Card from the Dresden tourist center at the hbf. We explained that we were going to Könegstein, and the person there, in addition to posts on is forum and the Rick Steves guidebook, indicated that the Regional Card was exactly what we needed. On our way back from Könegstein the conductor checked our card and told us that the card was only for Dresden and made us purchase tickets to return to Dresden. We were traveling with a native German speaker who tried to explain the Regional card to him, but to no avail.
The second time was when we attempted to use a group Bayern Ticket in Bavaria. After a much heated discussion with two different conductors and a ticket representative, I was finally told that the English version of the DBahn website is wrong. The upshot is that the group ticket does not include children, and the family ticket (which is only described on the German page) does not include more than two adults. So, if you're traveling with children both over age 18 and under, you can't effectively use either ticket. I was forced to purchase an additional individual Bayern ticket for my 19 year old daughter, and was offered no concession for the fact that their own website give incorrect information.
Next time I'm renting a car.