If there is a navigation label to change the name of the menu item this ignored by the translation.
The translation always translates the original page title and ignores the navigation label.
Nevertheless, WPML shows the name of the menu item correct with the navigation label in WP Menus Sync - but still translates the original titel.
So WPML seems to know what to trabslate and simply sends the wrong item to the translation.
It is not only a backend problem - WPML also shows the original page title instead of the navigational label in the front end of the translated pages (the orginal page works as expected and still shows the navigational label.)