Could not register -- is this a bug or a feature?

Question

On "2012-01-01 12:20" the answer which I was getting for
What is the output of "date -u +%W$(uname)|sha256sum|sed 's/\W//g'"?
on my system was different from what was expected by registration.
I replaced your expression with:
echo 52Linux|sha256sum|sed 's/\W//g'
and finally was able to register. Looks to me like a bug in registration.

Answer 1

It does not look like timezone issue because of '-u' option for 'date'.
From "man date" (GNU coreutils 8.5 February 2011):
%W     week number of year, with Monday as first day of week (00..53)
However I get:
date -u +%W
00
Good that
info coreutils 'date invocation'
has valuable addition:
Days in a new year preceding the first Monday are  in week zero.
So, it registration does not calculate correct week number. They probably do not use posted expression, or their tool uses is of different version. Probably this issue happens only at the beginning of new year before first Monday.
Still this could be a hidden quiz for new users...