Bug: Deselecting field changes from measure

Hi support,
 
I have a table with 4 fields, two of them numbers. When I click on fields, I see all 4 fields and the two measures have the SUM symbol next to them. If I deselect one, then close and reopen, it no longer shows the SUM symbol.

Reproduce:
1. Create Report with 4 fields, two of which are strings, two are numbers.
2. Go to Flat Grid View. Click on Fields, notice both fields are numbers in selector (They both show SUM symbol).
3. Deselect one number field and one string field so only one string and number fields selected.
4a. Close Fields Modal.
4b. (optional) Click Charts then Pie Chart. Notice is creates successfully.

5. Reopen Fields modal.
6. Notice that the deselected field no longer has SUM symbol.
7. Deselect the currently selected number field. Select the old deselected number field. (i.e. swap the selected number fields).
8. Notice that the SUM symbol still isn't shown. Close the modal. Open a pie chart again, it will error saying: "No measures to display. Add at least one measure in the Field List." However, there is a measure selected.
 
Expected Behavior:
When reopening the field selector modal, it should show "SUM" selector in Fields selector modal next to all numbers. Also, you should then be able to select Pie Chart and it should load correctly, just as it does when a number is first selected on table load.
 
Attached two photos showing the two states. "fields_1.png" shows initial state of fields. "fields_2.png" shows number field without SUM when reopen.