Map duplication error

Development World Creation
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4

It happens with clean project also, made in 4.14.P1. Steps are :

  1. New project
  2. Save level (NewMap)
  3. Duplicate map with Ctrl+W (NewMap2), and try to save project.

Then this message comes. If I press yes, it fails to do whatever it tries to do, and asks if I want to Retry, cancel or OK. Pressing Retry just loops the whole process.