Even as I unwrapped the package fell toward me a few smaller plastic fragments that were chipped off from the bottom corners of the side members. Because of the price I had this circumstance, as well as the cheap thin plastic, even unacceptable, because the function would probably not have been affected. So I am determined to take the building. Unfortunately, it was due to the mechanism despite the help of a second person is not possible to connect only two side members. Rather, we have cut our fingers on the sharp-edged plastic.
Fortunately, the seller Oxid7 performed the reversal correctly.
Another note at the end: We have alternatively resorted at the hardware store and the cost model, with about 25 even more favorable than this part, and lo and behold: The construction mechanism worked (albeit also fiddly) and we now have bought a second copy which serve their purpose well.