multi page webforms not working in webform as block

Steps to reproduce:

1. minimal Drupal 7 installation with webform enabled
2. in admin/structure/types/manage/webform/display set Webform to Hidden
3. create a new node of type webform
4. as form components add
   • textfield
   • page break
   • textfield
   • page break
   • textfield

   Leave all component settings at default

5. in node/1/webform/configure enable Available as block
6. in admin/structure/block move the webform block to sidebar second and leave everything at default settings
7. now call the page at node/1, fill out the 1st textfield and click Next Page
8. fill out the 2nd textfield and again click Next Page
9. Bug:you will not get to the 3rd page

As far as I understand it webform_node_view is called twice, the 1st call cleares the cache_form in drupal_process_form and hence the page_num information is lost for the 2nd call (that uses the same form_build_id to fetch the cache_form).