I've had several packages containing CDs sent via Tenso, and none of them have had any damage (and my packages have to go a really long way to get to me, before meeting the Swedish customs which makes me surprised at the lack of damage to packages I've got
). There's always a risk, even when using large amounts of bubblewrap and such, that an item will suffer damage either due to improper handling or for random reasons (the tape didn't hold the item properly, the item was pressed too hard against another item in the package, etc.). While I'm certain that Tenso can make mistakes when it comes to their packaging, I wouldn't let one incident dictate my decision to use them. Most likely, this incident was a one-time thing and not a trend on Tenso's part.
Though asking Tenso to increase the padding inside their packages if you're worried is good advice as well.