Custom Functions - Bug

JavaScript Custom Functions do not work with What-If Analysis (Goal Seek)

link - github.com/OfficeDev/office-js/issues/4745 

JavaScript Custom Functions do not work with What-If Analysis (Data Tables)

link - github.com/OfficeDev/office-js/issues/5940 

Enter the values in cells B2, C2, B3, C3
Enter the formula "=SUM(C2,C3)" into cell "B7"
Enter the numbers 5, 10, 15, 20 across in row 7
Enter the numbers 3, 6, 9, 12 down in column B
Highlight cells B7:F11
Select Data tab, What If Analysis, Data Table
For the row input select cell "C2"
For the column input select cell "C3"
Press OK - The data table will be populated correctly

Now lets repeat this using a custom function that adds up two numbers
Enter the values in cells H2, I2, H3, I3
Enter the formula "=CUSTOM.ADDFUNCTION(I2,I3)" into cell "H7"
Enter the numbers 5, 10, 15, 20 across in row 7
Enter the numbers 3, 6, 9, 12 down in column B
Highlight cells H7:L11
Select Data tab, What If Analysis, Data Table
For the row input select cell "I2"
For the column input select cell "I3"
The data table is not populated and a calculation error is displayed