[Averton (P and C)]

Not strictly a DIY project but hopefully the DIY people will have the answer. We purchased a cheap 0.5x focal reducer which when we used it had the most awful image imaginable. All stars had a flare coming out one side that made them look like small street lights. When we disassembled the reducer it had 2 elements cemented together. One is a normal looking convex lens and the second is concave on one side glued to the lens and flat on the other side. The elements were mounted in the holder so that the convex lens faced the camera or eyepiece and the flat side faced the telescope/subject. This appeared incorrect to our thinking so we reversed it and have only had one chance to test it thus far but it was a huge improvement. No more flaring.
Questions - which way round is the correct way? Is it possible that the manufacturer assembled it incorrectly or didn't know the correct way around? Pictures on line of this reducer seem to show the elements mounted as supplied to us it does not appear to be a one off mistake.
Thanks for your help.
Peter & Clare