Symptoms
You create a business rule that uses the "must be unique" action for an attribute by using SQL Server 2014 Master Data Services. When the given attribute is null or blank, the "must be unique" action may be evaluated incorrectly.
Resolution
This problem was first fixed in the following cumulative update for SQL Server:
Cumulative Update 1 for SQL Server 2014 SP1 /en-us/help/3067839
Cumulative Update 7 for SQL Server 2014 /en-us/help/3046038
Each new cumulative update for SQL Server contains all the hotfixes and all the security fixes that were included with the previous cumulative update. Check out the latest cumulative updates for SQL Server:
Status
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.
References
Learn about the terminology Microsoft uses to describe software updates.