Creating a new replication job with custom ID shows a non existing conflict

[calonso]

Expected Behavior

1. Login into Fauxton
2. Open the Replication section
3. Click New Replication
4. Fill in the data and write a custom ID for the Replication Document field (make sure it doesn't exist yet)
5. Click Start Replication
6. You're asked for your account's password
7. The replication job starts

Current Behavior

1. Login into Fauxton
2. Open the Replication section
3. Click New Replication
4. Fill in the data and write a custom ID for the Replication Document field (make sure it doesn't exist yet)
5. Click Start Replication
6. An error box appears claiming that the custom id you just entered already exists and the document will be overwritten.
7. You accept the document to be overwritten
8. You're asked for your account's password
9. The replication job starts

Your Environment

• Version used: 2.1.0
• Browser Name and version: Chrome 60.0.3112.113 (Official Build) (64-bit)
• Operating System and version (desktop or mobile): Mac OS version 10.12.6

[linkit-odoo]

I verify this behaviour in 2.1.1 (apache/couchdb docker image) Further, if you do not specify a custom ID, you will not incur in the aforementioned message, but your replication document will overwrite the existing one.