Add or Remove input variables for WS operation not working correctly

The variables are now shown after opening the model, however, clicking Add or Remove variables shows the Edit Input Variables editor with all the variables deselected. Selecting some of the variables adds them to the transformation, resulting in invalid SQL.

New steps to reproduce:

import the attached project
double click the OrderCheckingWs in model explorer, the model editor will open
click Add or Remove variables
notice all variables are deselected
select OrderDate, click OK
save the model, the following validation error is shown:

ERROR: Variable VARIABLES.IN_OrderDate was previously declared.

Note that as a user checks/unchecks variables, the SQL transformation is trying to keep pace with the selections and isn't staying in sync. You can end up with multiple/duplicates. Expanding the tree shows that 2 of the 3 variables show as checked. But OrderDate is Not.