This question has been answered by multiple community members. See the first response.
It could be your browser cache. If the name of the file and the folder are precisely the same then it would have overwritten the file, if you are still seeing it, then it must be in browser cache.
and the precisely same url is getting different images in ftp and regular? Hmm I have seen some lag when making changes in designs before, but clearing cache should solve them.
Again, if the one image file has overwritten the other, then the overwritten one can only come from a cache somewhere, because the picture file doesn't even exist anymore.
Could it be a cache from your hoster? Does ftp have a cache? I just don't see how this is possible.
Can you post a URL to the page in question?