REPLACE ALL OCCURRENCES OF REGEX

Hello, Below statement is not working in my program. REPLACE ALL OCCURRENCES OF REGEX '[!@#$%^&*+-= ]' IN wa_var1 WITH '_'. eg : wa_var1 = 3-ROW SEAT then output should have been 3_ROW_SEAT but instead the Output is giving as __ROW_SEAT. This statement used work before all of a sudden this statement is acting weird in our program. Could anyone please provide your inputs. Thanks....