Bug overview description.
Trying to upload this image from the .jpg URL
http://www.furaffinity.net/user/zafara/
http://www.furaffinity.net/view/26169658/
http://d.facdn.net/art/zafara/1516890156/1516890156.zafara_%D0%A0%D0%B8%D0%BD%D0%B0.jpg
results in this error
Error: Source couldn't be opened: HTTP error code: 404 Not Found

What part(s) of the site page(s) are affected?
Uploading

What is the expected behavior?
Uploading from a FurAffinity URL should always work.

What actual behavior is given instead?
Uploading from this particular FurAffinity URL results in an error.

Time of incident (if applicable).
just now :)

Can you reproduce the bug every time?
yes

What steps did you take to replicate this bug?
see above

Errors or other messages returned (if any).
see above

This might be a unicode issue, I haven't confirmed this yet, but the uploader might be seeing the url as:
http://d.facdn.net/art/zafara/1516890156/1516890156.zafara_Рина.jpg
instead of: http://d.facdn.net/art/zafara/1516890156/1516890156.zafara_Рина.jpg

Although the site is written in Ruby, JavaScript has a good example improper decoding of URLs:

> unescape("https://d.facdn.net/art/zafara/1516890156/1516890156.zafara_%D0%A0%D0%B8%D0%BD%D0%B0.jpg")
< "https://d.facdn.net/art/zafara/1516890156/1516890156.zafara_Рина.jpg"
> decodeURIComponent("https://d.facdn.net/art/zafara/1516890156/1516890156.zafara_%D0%A0%D0%B8%D0%BD%D0%B0.jpg")
< "https://d.facdn.net/art/zafara/1516890156/1516890156.zafara_Рина.jpg"

I can confirm that almost every time there's URL with russian or japanese in it, the upload simply fails.
However I usually simply just download the file into local machine and upload it regularly.

I used to overcome this issue by replacing the random percent-encoding part with the actual "Рина" into the link.

Рина is cyrillic Rina. Doesn't necessarily have to be Russian.

Bug confirmed, doesn't work on copy-paste.