I met the same problem on OS X 10.8.4 and Geforce 320M or Radeon HD 6970M
As a workaround, I replaced an argument which receives a value by one which receives reference(that is a buffer object).
I could get member values correctly. But if it contains an array as its member, I couldn't get each component of the array.
I know this thread is no longer new, I post this report
There is still the problem.