FSA Annual Limit Exceeded with Arrears Payback

The FSA a/c has an annual pledge amount of $2700 entered.

I have an employee that had FSA go into arrears for $61 on the paycheck since there wasn't enough net pay.(3/01 to 3/15 paycyle)

Had there been enough net pay the $61 would be taken and the YTD met.

On the next paycheck,(3/16 to 3/31) the PayCalc took the remainder of $61 and also took the $61 that was in arrears payback thereby going over the Annual Pledge amount.

Now, the YTD shows $2761 and annual pledge shows $2700 !

How did this happen? Shouldn't it have stopped and given an error during the Payroll calc?

On the next payroll calc (4/1 to 4/15) it did give an error and thats when we caught it!