Note that when you continue the previous question ('partman/continue'), the installer moves on to the timezone page. I think that's part of the issue - this page can't handle the dialog. Also the question name ('partman-efi/non_efi_system') isn't matched by the list of expected questions, but I didn't find out yet if that's a problem because I don't know atm how to solve the first bit.
I tried a bit to look at this.
Note that when you continue the previous question ('partman/ continue' ), the installer moves on to the timezone page. I think that's part of the issue - this page can't handle the dialog. Also the question name ('partman- efi/non_ efi_system' ) isn't matched by the list of expected questions, but I didn't find out yet if that's a problem because I don't know atm how to solve the first bit.