You are right; the design is not perfect. The velcros, however, SHOULD attach either to the frame of the seat unit (but it's not made so that it allows it, I believe) or around the joint where the attachment points are. I personally would try to wrap the velcros around the central joint OR at least the bumper bar sides. I also think that it is not best to leave it just like that. Also, if nothing works, I would try to CONNECT the two velcros under the seat to secure it that way.
The Hauck strollers are the low-end ones, though, so you need to take that into account when thinking about the design - they are made in China, for a very low price, so that it is primarily affordable. I found more design flaws like that with their products.