Download problems with Safari on macOS

If I download some files with Safari on macOS (10.12.3) the filenames are getting some strange modifications.

e.g. a PowerPoint file named like “abc.pptx” is downloaded as “abc.pptx.ppt” (the .ppt extension is added)
or a PDF file named like “a b c.pdf” is downloaded as “a%20b%20c.pdf”

If I’m using Chrome everything is working fine.

Any idea?

No one else having this problem?

%20 is an url encoded space. Looks like Safari does not decode it. How it should be encoded can likely be found in an RFC.

No. The space is not the problem. The problem is the added ppt extension!

Do you use something like save as dialog, or is the file being saved automatically as it usually is using chrome?

It’s saved automatically.

I can confirm that downloading .pptx-files from seafile with safari results in a added ppt-extension. Quite strange. If you download a pptx from another location (for example: http://dev-builds.libreoffice.org/tmp/test.pptx) nothing else is added.

Does anyone know how to use the developer tools? Would be interesting where these downloads differ. Could imagine it’s due to the mime type.