This is one is harder to reproduce.
Basically, when submitting the create page form it will simply reload, without doing anything. Submitting the form a second time works and properly takes you to the new page in edit mode.
As far as I have been able to debug it at some point, I remember concluding that the XWiki Select widget fails to set in time the templateprovider parameter (from the document type you have selected) and, when you submit the first time, your request is sent without it. Thus, the CreateAction will not move forward, since it`s missing this mandatory field. Submitting the second time seems to give enough time to the Select Widget to do its job and build the correct request.