(At least I am assuming it is the braces.)
Example url: http://www.flickr.com/photos/smithsonian/11068139743/in/set-72157638081157985
Error message: Could not understand the file name "[View of automobile by campsite] during deer season at Hardy Ridge [Washington], October 1949.jpg".
After clicking the error away, there is no button to upload a different image and the user has to start from the beginning, but that's probably a more general bug.
Version: unspecified
Severity: normal
See Also:
https://bugzilla.wikimedia.org/show_bug.cgi?id=64912