To reproduce this issue :
- Start a SonarQube 4.2 (or previous) server and stop it
- Start a SonarQube 4.3.X server with a incompatible plugin (For instance PHP 1.2)
- Execute the migration (/setup url) -> the server will fail but the migrations will be done
- Restart the server without the incompatible plugin
-> Requirements won't be copied to rules and will still exists in the characteristics table.