It's not wrong. There are multiple ways to represent a lot of filenames (in particular, names with accents, umlauts, or graves). It's very plausible that the input methods on different systems are producing different sequences (composed vs decomposed). If you're storing a file with a composed sequence on your server, then copy it to your Mac's drive, then copy it back, you may end up with a duplicate file because it would have ended up as a decomposed sequence on your local drive.

But this doesn't make it wrong. You can reproduce this exact behavior with other systems too simply by changing the local filename to be decomposed. The only Mac-specific part here is that HFS+ will automatically decompose the filename.