__RequestVerificationToken always the same when reloading form in MVC4 application

__RequestVerificationToken always the same when reloading form in MVC4
application

While on a development server a standard MVC4 / EF4.5 login form with
Html.AntiForgeryToken() refreshes its value with every page load. When
deploying the same code on IIS the hidden value __RequestVerificationToken
is always the same (at least in one browser session). Other similar
applications on the same server do not seem to have this behavior.
Which web.config/IIS parameter might be responsible for this?
Already tried setting the machine key (single server) but this only seems
to shorten the token, the refresh problema remains the same.
Also tested in different browsers. Here are some demo values for IIS and
development server:
IIS:
Without machine key in web.config:
BGxqV7DjpHomi22By0r70WebHiWMV2OcsrCMN-dNDkRElZrv6BMQH23_zK9abmRsty_n1NImH2-gEsi3nBrWIQ2
With machine key in web.config:
dXBdht7mn2plT2rPvv0HzWtFvn-N9MT6xzW_xc8dVqnLdofzrL5v0SZFMAFPTANR0
Cassini / development:
Without machine key in web.config:
Yedkrxms9oYmHGzhV93qsrryVuNKZSWKBwCkP-RzK-tAZGgQ6J5g6Yp0LsCQPehucVwDcUs5lfRUf6Y6FxYUqY0olkE3-PmtF0ZnrCcbXD6XuA1PgPoFchreTPnCCSCwsh3E3FPmdKPlabyOfqiykkVqocxzYBMqd7A3bCZIxU01
With machine key in web.config:
iFjqi1OYplYfhCYdflAw1LSncVwK3b1yfDaJRgfrqVamucJ992D3-pFD__RolMZ_edp6muXQWLkxGOQp5Wn2ObTKXltO2J9tq32-JUMGu7cXdYZMkty3MRwuE-SuIFt7zo7TvQ2