The field only HAS one value, since it is a maximum at the report level. If you want to see a maximum per some group, you have to add a group condition, as in:
Maximum({@Explanation},{table.groupfield})
If adding the formula changed the number of rows, it probably means you are using more than one table, and the formula was the first reference to the second table. To maintain the same number of rows, change your join to a left join FROM the first table TO BUSINESS_RULE_VIOLATION_VW.
-LB