good question that deserves being tested

I have not done so, but I guess that if only one of your triggers is fired (due to the WHEN clause), there won't be any problem, but if you update a and new.status = 'M' and both triggers should be fired, there are chances that the second trigger's execution will fail with error ORA-04091: "table %s.%s is mutating, trigger/function may not see it"...