1. Create event correlation with two conditions (for example values "test1" and "test2");
2. with type of calculation set to "And/Or", observe the expression is calculated "A or B";
3. save it (this is important step);
4. open to edit it;
5. add another condition (for example "test3");
Result: calculated expression is sometimes "(A or B) and C" and sometimes A and (B or C);
Expected: A or B or C

In 6.0 it works fine.