Filenames not normalized? (Umlaut issue)

There seems to be an issue with German Umlaut characters (ÄÖÜäöü) when Macs and/or the Seafile Client are involved.
I’ve created a folder structure in a library by extracting a ZIP file using 7-Zip. The ZIP was created on a Mac. I’m using a Windows PC. After unpacking the ZIP file, I sync’ed the top folder with the Seafile Client. Everything worked fine so far and this saved a lot of time by not having to create the structure manually. Unfortunately, folders which contain Umlaut characters are not accessible. They are visible but it’s not possible to upload files into these folders. What’s worse is that it’s not even possible to delete or rename these folders. If this is done via the server’s web interface, there’s no error message but the folder simply stays. Deleting the folder from the local filesystem and sync’ng doesn’t help either.

As far as I can tell, the root cause is the UTF-8 normalization used on Mac filesystems (NFKD) which encodes these Latin-1 characters as two codepoints (base character plus modifier) whereas everything else uses UTF-8 NFC which encodes these as compact single codepoint characters. So while both strings are supposed to be logically equal by Unicode rules not only do the binary representations differ but the codepoints as well.

Since I’ve been using Seafile Server for quite some time and didn’t run into this problem when using the web interface, I suspect using the Seafile Client caused this issue to appear. My questions are: Is this a known bug in the Seafile Client? Is it possible to get rid of the unusable folders without deleting the whole library?

Seafile Server 6.1.1 (Debian 8 with nginx/1.9.10)
Seafile Client 6.1.0

I’ve not run into issues with umlauts (or any other character) so far. Could you share that zip or a minimized version having the same issue? I could test it and see what happens.

You can also share it privately with me at https://home.hoeper.me/u/d/158a1dbdfeed4496bbee/

(note that although I’m moderator, I’m just a community member as well)

Sorry for my belated reply. Thanks for trying to help! I’ve uploaded the file (Archiv.zip) using your Seafile upload link.

After unpacking the archive on my windows system the filenames are immediately broken.

Edit: After unpacking them with 7zip it works. They are being synchronized.

Uploading a file to them with Seahub fails with 400 error "“error”: “Parent dir doesn’t exist.”. Looks like the upload request is wrong.

Navigating works.