Unwanted Noise element during dilation

I'm applying the dilation operation on a binary ricegrain picture. When the structuring element used has size 9x9, the noise particles get enlarged, which is logical. But when I use a structuring element of size 15x15, i get new noise particles adjacent to the original noise particles. This is vry confusing as i can't why this is happening. The stucturing element is a nxn matrix with all 1's. The images have been attached for reference.

Reference image: http://ift.tt/1FsvjWU

Dilated image (9x9 SE): http://ift.tt/1FsvkKy

Dilated image (15x15 SE): click on third image in previous link

Please help!!