I create the following casacading select:

List 1
option1.1
option1.2
option1.3
List 2
option2.1
option2.2
option2.3
List 3
option3.1
option3.2
option3.3

When I create an issue everything is fine. I then make this a required field I then see the following at issue creation:

List 1
none
List 2
none
option1.1
option1.2
option1.3
List 3
none
option2.1
option2.2
option2.3

I can switch back and forth between making the field required and optional. Whenever it is optional everything is fine. Whenever it is required I get the above.