score:4
You do still receive the 50% MQM bonus on top of the minimum 500 miles, resulting in 750 MQMs earned for the flight. So, the formula is:
maximum (500, distance flown) * 1.5
Here's how my flight from yesterday (May 19, 2015) was credited:
For reference, BNA->ATL is only 214 miles. So, they did apply the 500 mile minimum first and then apply the 50% bonus, yielding a credit of 750 miles for the 214 mile segment.