This is a minor "bug"-- I put it in quotes since it's obviously the programmed behavior, however, if you have two fields named the same, one in the Nodes table, and one in the Interfaces table, there is no way to visually distinguish the two in the 'Edit Alert' (i.e., "Trigger Condition" edit box). See image:
As you can see in the image, there are two entries which both say "Critical is equal to Yes". This is NOT a duplicate reference! Rather, the first one is the 'Critical' field assigned to the Nodes table, and the second is the 'Critical' field assigned to the Interfaces table. The suggested fix is to simply prepend the appropriate table reference in the editor to make it obvious what is happening.