"Enable preview page" not respected.

I have a form with two pages and the second page is shown depending of the value selected in the first page.
The option "Enable preview page" is unchecked.

Case 1 (works as expected):
If the selected value of the first page is 0 the second page with a textfield and the "Submit" button is shown. On the second page the button "Submit" sends the form as expected and the "confirmation screen" is shown.

Case 2 (doesn't work as expected):
If the selected value of the first page is 1 the form must be directly submitted and the "confirmation screen" must be shown. But in this case the Preview page is shown instead of the confirmation page.

It seems that the option "Enable preview page" ist not respected. Is is tha expected behaviour?

Webform version: 7.x-4.10
Drupal: 7.39

Thanks in advance.