Hi,
It was not a known behavior until you pointed it out, so thank you for that! A defect has been opened so that we can fix this in the template. You can correct it on your own, however, by updating the script that does this calculation. To do that, you must use the Eclipse client and follow these steps:

1. Establish a Repository Connection to your RTC repository
2. On that connection, choose Manage Connected Project Areas... to access the project area
3. Open that Project Area and then choose Process Configuration
4. In the menu, navigate to Project Configuration > Configuration Data > Work Items > Attribute Customization
5. In the Attribute Customization box, expand Calculated Values to find Calculated Achieved Value
6. Update the script to only do the calculation if both the planned and actual values are non-zero:
   

                    var achievedValueRatio = 0;
                    var achievedValue = 0;
                    if (busValPlanned > 0 & busValActual > 0) {
                           achievedValueRatio= Number(busValActual / busValPlanned);
                        achievedValue= achievedValueRatio * 100;
                    } else;

Let me know if you need any help with this and thank you for pointing out the issue.
Amy