URGENT: Workflow working partially

I've built a small workflow on "Close Date" field under Opportunity that one can't put the back-dated date. It was working normally however I noticed an awkward behavior in a scenario when year shuffles.

Workflow: PRE('<CloseDate>') <= [<CloseDate>], Message - Close Date cannot be back-dated.

Example:

Close Date: 25-Dec-2012

Changing this to back date, it throws the above error and simlutaneously if i put any future date, it accepts normally (But only if the future date lies in the same year i.e. till 31-Dec-2012). As soon as I put-up the futue date of next year, still above error message gets displayed.