We set up an event that lets people signup on line. The dedupe rule we used on the event is first name, last name, email address (all need to match). A few of the signups created a new contacts, meaning for some reason it didn't find an existing person, but when I looked at these people I find that there is already a contact with the exact same names and email addresses. There are plenty of other people who registered for the event where it found an existing contact to match to.
I thought, well maybe, something isn't exact and went to Find and Merge duplicate contacts. I used the exact same rule. It finds the duplicates.
So why does the rule work sometimes and not other times?
Out of 21 registered 18 already existed. 12 of the 18 matched a record. 6 of the 18 created a duplicate contact.
One guess is there is some trimming going on after the dedupe rule is used. I suppose I can try to test for that.
CiviCRM 4.6.26, Drupal