The fact that Juwel offer replacement Brace Bars would suggest that it is a design fault. Juwel Aquariums are excellent but design faults should not be paid for by customers.
i purchased these as i bought a second hand rio 400, it did not have any brace bars on it, i contacted the supplier and asked are these what a new tank would have on,he said yes, so i ordered them,when they arrived they were not as thick as originals but i fitted them anyway,they have been on my tank a while now and appear to be doing the job,my tank holds 450 litres. as of now i would recommend these,would not hesitate to buy again.