Open a regular expression for editing in one tab, then delete it in another. In the first tab, attempt to save. Observe a whole bunch of SQL errors:

Error in query [INSERT INTO expressions (expressionid,regexpid,expression,expression_type,case_sensitive,exp_delimiter) VALUES (88,6,'??3',0,0,',')] [Cannot add or update a child row: a foreign key constraint fails (`issue_zbxnext_889`.`expressions`, CONSTRAINT `c_expressions_1` FOREIGN KEY (`regexpid`) REFERENCES `regexps` (`regexpid`) ON DELETE CASCADE)]
Error in query [INSERT INTO expressions (expressionid,regexpid,expression,expression_type,case_sensitive,exp_delimiter) VALUES (89,6,'??',0,0,',')] [Cannot add or update a child row: a foreign key constraint fails (`issue_zbxnext_889`.`expressions`, CONSTRAINT `c_expressions_1` FOREIGN KEY (`regexpid`) REFERENCES `regexps` (`regexpid`) ON DELETE CASCADE)]
Error in query [INSERT INTO expressions (expressionid,regexpid,expression,expression_type,case_sensitive,exp_delimiter) VALUES (90,6,'??',0,1,',')] [Cannot add or update a child row: a foreign key constraint fails (`issue_zbxnext_889`.`expressions`, CONSTRAINT `c_expressions_1` FOREIGN KEY (`regexpid`) REFERENCES `regexps` (`regexpid`) ON DELETE CASCADE)]