Although the accent on nouns is persistent (it tries to remain over the same vowel or diphthong), it may be forced towards the end of the word if the length of the last syllable (the ultima) changes. This is what happened here. If the ultima of a word is short, the accent is allowed to be on the third-to-last syllable (the antepenult), but if the ultima is long, the accent cannot fall further back than the second-to-last syllable (the penult).
IPHIGENIE: Kann uns zum Vaterland die Fremde werden?
ARKAS: Und dir ist fremd das Vaterland geworden.
IPHIGENIE: Das ist's, warum mein blutend Herz nicht heilt.
(Goethe, Iphigenie auf Tauris)