After playing around a little bit more with the ubuntu-package and editing the file
/usr/Brother/inf/brMFC5440CNre
manually and setting PaperType=A4 instead of PaperType=Letter
it works like expected and the test page is actually printed using A4. So that's where the Problem lies.
Will try to test the original Brother packages now after Till's advice (Thanks!).
After playing around a little bit more with the ubuntu-package and editing the file
/usr/Brother/ inf/brMFC5440CN re
manually and setting PaperType=A4 instead of PaperType=Letter
it works like expected and the test page is actually printed using A4.
So that's where the Problem lies.
Will try to test the original Brother packages now after Till's advice (Thanks!).