If you are calculating the match on a payroll basis (don't confuse calculation with deposit), then you will never use compensation over the limit, unless the pay for that period is in excess of $285,000 (I want that job!). If the comp did go over the limit that pay period, you should restrict the compensation to the limit for that pay period.
Also, it is good policy to put match caps in place in your payroll system. If it's dollar for dollar up to 5% of pay, you instruct the program to cap the match at $14,250.
If you are calculating the match on an annual basis, then you are already (or should be) capping the formula with the max comp.
Kevin, what would you do in the case of someone who makes $$600,000 a year and decides to put in her deferral in the last payroll of the year, or out of the late-September bonus check? Does she not get the match b/c she passed the cap sometime in July?