I have recently upgraded our 2007 envrioment to 2013 and afterwards a few of our libraries are having trouble grouping on a calculated column. The year column is calculated using the following formula ( =TEXT([As of Date],"yyyy") ). When a document is added or edited in the library the year group it was in gets duplicated as in the screen shot below. I can fix the issue be re creating the calculated field and fixing the view, however as soon as a document is edited or added it starts all happening again.
Any Ideas?