Effective in version 10.5, Test Data Management uses an updated algorithm to optimize dictionary usage in Substitution masking. When you choose the Optimize Dictionary Usage option in a Substitution masking plan the plan uses the updated algorithm. The algorithm ensures better use of dictionary values in masked output.
To ensure backward compatibility with plans created previously, and to generate consistent masked output after upgrade, you can create a project property to choose to use the previous algorithm. Set the property value to true for projects that require backward compatibility or to false if you want to use the updated algorithm.