Test case on GardenWorld:
On BP field of sales order right click and create new
Fill BP search key with "C&W" (this is an existing search key)
Fill the rest of fields how you prefer and push the OK button
Correct -> an error message appears stating: Could not save record - Require unique data:
Please change information.: ERROR: duplicate key value violates unique constraint "c_bpartner_value"
Detail: Key (ad_client_id, value)=(11, C&W) already exists.
Now correct the BP search key with anything different (i.e. XYZ) and try to save again.
Wrong -> a window telling SaveError appears and you cannot save the BP