There is no such a bug in our code and the options for this error are changes in the database tables, stored procedures or you have two or more different versions of Sitefinity connected to the same database. The transactions are controlled by data layer and since there is no bug in our code related to "duplicate primary" keys in the database, you have made some changes without using the API to cause it.
You can observe [sf_CmsContentBase] table to find the duplicate entry and try to remove it. Then re create the same content again and see whether the issue will appear. You can use SQL Profiler to see the actual queries to the database.
All the best,
the Telerik team
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