Adding Elements to multiple Struct Arrays of a specific variable type is unreliable

Adding Elements to multiple Struct Arrays of variable 'Slate Brush' is unreliable.

1. Open a new blank bp project
2. Create a new Struct & open it
3. Add five Variable of the 'Slate Brush' type
4. Save
5. Under the Default Values, click the + in secession for bottom to top

Results: Elements will not always be added when the + is clicked (once elements are added press the Trashcan icon, all the elements on all variables will be delete)

Expected: For the Elements to add and delete on click