POSTs and the back button

Scope: One or more POSTs are performed e.g. on a form that has the current URL as its action attribute...

Symptoms:

In case of GETs, everything seems to be alright
On multiple POSTs and then pressing the back button multiple times, the effect is not as desired (no page change at all is performed).
It works in case of GETs because the URLs in the history change. Not so, however, in the case of POSTs - the URL history contains identical URLs.

Example (Please submit the form in the content area multiple times with diffferent values and then press the back button repeatedly)

Any ideas, what is causing the above behaviour?

I suspect that this bug is specific to the example and on the server-side setup of www.oeko-fakt.de...

Thanks in advance!

arvgta / ajaxify