In a possessive structure like this, (noun)+(μου/σου/etc), if the noun is stressed in the third syllable counting from the end of the word, we also put an accent mark in the last syllable and pronounce both accents. So we have: το πουκάμισό σου, το φόρεμά της, το κοτόπουλό μας etc. In the last four syllables of the phrase the voice goes ...-up-down-up-down (like saying "very silly") and the main stress is the second one. (Reported it)
You're right, but due to technical problems we can't add two accent marks in the basic sentence. We have added it as alternative.