I have about a dozen sites running on the same virtual server(all running the same version of everything). Half have this problem, and half don't.
When I go to the wordpress dashboard and click on settings/sitemap xml it hangs and doesn't display the second half of the page so I can't modify the setting on the bottom of the page.
Here is a screen shot of where and how it gets stuck.
Ya see it is the sitemap.php file that hangs. It is this way in the production version and the current beta.