Duplicate Detection Rules can use lookups

I recently configured a duplicate detection rule that used a lookup field as the match field.

I was surprised that at first duplicate detection did not appear to work when adding duplicated records. I had checked that the entity was enabled for duplicate checking and published the rule.

However, after a while, I found that the duplicate detection rule did work. So even if the rule has a status of published (which means that all the matchcodes have been generated) there might be a delay before it works.