I have just notice that the reports we have that summeries in weeks and state a week number is one week off, because there was a week 53 between 2009 and 2010, see attachment.
I found this blog post http://www.garyrgilbert.com/blog/index.cfm/2010/1/4/Yes-there-is-a-Week-53 which suggest that its a MSSQL issue.
Did other notice this and is there a work-around?
ISO defines a 53 week year. We have been using Gregorian week numbers but I'll place this in the bug tracking system to switch to ISO.