Changing global $language has (nevative) side-effects

I tried to use admin_language on a multi-language site, which worked fine at first.

After editing some nodes I noticed a big problem: As the global $language-variable gets changed I get redirected to as somewhat mixed URL, meaning:
I edit /de/node/116 -> Admin changes language to "en" -> If I save I get redirected to /en/node/116

Now, the URL includes the wrong language, which for example stops the menu from working. (as no menu exists for that node in the selected language)

Perhaps this is related to http://drupal.org/node/621426, as I get redirected to /en/node/116 even if the original node had an alias (meaning: /de/ein-node-alias -> /en/node/116). I think this is because no alias exists for that node in (global) $language. If you follow your links to that same node the alias is there, it only cannot be used as the form-redirect as global $language was modified and no alias exists for that language.