Regex filter broken in Search Builder
It would appear that the Regular Expression option in Search builder is broken. This can be reproduced by doing a search builder with the regex expression of [A-Z]{2}$ for the first name. It will pull up any contact that has 2 letters. This is because the regular expression gets transformed into lower case and also REGEXP / RLIKE isn't case sensitive by default unless used with the word BINARY
Original issue: https://issues.civicrm.org/jira/browse/CRM-21617