This is a subtle issue. Windows platforms are case insensitive, so the file (or folder) "aBc" is internally the same as one named "ABC" or "abc."
When archiving folders and files, SpiderOak preserves the case of files exactly as they exist on the filesystem.
However, Mac and Linux are case sensitive, so on those platforms those would be three different files. Suppose you backed up a folder containing those three files on Linux, and then tried to download that folder on Windows: SpiderOak would not be able to restore that folder in the same way on Windows. As soon as SpiderOak created the first file "aBc," it would not be able to create a second file named "ABC", because that filename already exists. So, in that situation, there is no way for SpiderOak to restore the downloaded folder exactly as it was. The folder would restore with the original case if it were downloaded on a case insensitive OS, however.