TYPO3 Core

When editing or creating new content in the backend typo3 will throw the following error:
You don't have permission to access /typo3/alt_doc.php

There are of course many ways to make a new record and to edit a record, there are some ways in which the error will not show up but the behavior is always consistent. The following flow is one of the many ways to produce the error: List mode, create new record button all the way on the top, "Click here for wizard!", text element, normal column -> error.
Other flows can be seen in the attached swf.

The problem does not exist in typo3 4.3.2! When I switch back to 4.3.2 the problem is gone.

(issue imported from #M14698)