Details can be found in the discussion:

https://access.redhat.com/discussions/5306951

 The path where to store a document is composed of

• document store path
• document id
• document name

as can be seen in the source code.

So it should look like

.docs\388f4d34-b732-48d6-b898-d00fd8bb1cf3\a.pdf

However, on Windows the whole path of the document is taken from the form as a document name which causes a malformed URL to be created:

.docs\388f4d34-b732-48d6-b898-d00fd8bb1cf3\D:\test\a.pdf

I have tried the same scenario using Fedora and there is just the name displayed upon uploading, so it works on Linux correctly, see the screenshot.