Tags are key:value attributes, and any given attribute of a node (line) can only have one value.
From FT’s point of view, that line would mean ‘the contact of this node is Karen’, and then when you respecify the contact attribute of that node as ‘Eric’, it simply replaces the earlier assignment, which can no longer be treated as a tag.
Perhaps, for example: @contact-Karen@contact-Eric ?
OK, I see. I’d prefer to be able to filter based on either lines containing the key “contact” or contact value “Karen,” but I’ll think about other ways to do that.