Hmmm... Right now (Sat Oct 24 00:36:56 CDT 2015) on my Arch Linux system there appears to be a problem with the date command:
$ date -d "+8 days" "+%A %d %B %Y" Sunday 01 November 2015 $ date -d "+9 days" "+%A %d %B %Y" Sunday 01 November 2015
I am using this in a script to display my schedule on my desktop that this error causes to print Sunday twice on. I know I could fashion a workaround, but a core utility like this should be working correctly, no?