R2014a slower than R2013a

On the same computer, when running imdilate, R2014a takes 4.1 sec while it was 3.7 sec on R2013a. this is consistent after multiple runs.

se = strel('ball', 4, 4, 4);
bw = imdilate(im, se); % size of im: 512*512*375

Also, why imdilate returns a new matrix with min and max value of 4 and 5, respectively, instead of anticipated 0 or 1??