While there's ample evidence the the Soviet Union copied a lot of details of our Shuttle when creating the Buran, there were also some very substancial differences in the designs. In one of my books at home, I have a picture of a Soviet space plane model being wind tunnel tested. It looks very much like the Shuttle, but the picture was taken in 1965. Hypersonic aerodynamics had a great deal to do with the configuration of both vehicles.

Even on a much simplier level, look how similar the Boeing 707 is to the Douglas DC-8 to the Convair 880. All three planes were designed to meet roughly the same requirements at about the same time.

Later, similar designs were used for the Boeing 767 and the Airbus A-320 as well as the Airbus A340 and the Il-96. Even planes as simple as the Beech Duchess and the Piper Seminole and the Beech Skipper and Piper Tomahawk are very similar. No one is seriously suggesting those companies copied each others designs or stole the designs.

Then again, some designs are just wierd, like the Polish PZL M15 Belphegor, a jet powered biplane cropduster or almost anything designed by the master engineer, Burt Rutan. He probably couldn't design a normal looking plane if he tried, but then, who would want him to?