SQL Server Merge Replication Computed Column Conflict Resolution

I'm setting up a merge replication web publication for a table that needs to use the DateTime (Later Wins) conflict resolver so that the most recently modified row wins in any conflict. This table (and hundreds of other tables) use a datetimeoffset for their modified date as subscribers can be in many timezones. In order to get the required datetime value as a column I've added a ModifiedDateUTC datetime computed column which does a simple CONVERT to a datetime. The issue I'm seeing is that even though the article setup accepts this as a valid column, whenever I generate a conflict I get the error 'The specified conflict resolution column 'ModifiedDateUTC' could not be found.'