I have the exact same problem. I am in Düsseldorf, Germany and only the marketplace of Facebook locates me in Louisville, Kentucky US - when I try to change it and use the positioning button on the map it brings me to Düsseldorf, when in leave the map it still reads Düsseldorf and when saving the offer it changes to Anywhere else in Facebook where in have checked my correct address/ location is used. Normal posts etc, all good. People nearby: works great.
I also noticed, when I look at my marketplace posts, it shows Louisville, Kentucky (40217) next to my post - the numbers in brackets are the zip code of Düsseldorf - and no, Google did not give any hint that this zip code is also used for Louisville - not even similar zip code there..