• Affects up to build 4
  As is expected, an opaque block on a grass will turn grass block into dirt. This process should be done in a few "random tick"s. Covered with cobblestone, however, 3 in-game days (60 minutes) had passed but no grass block turned into dirt. (In the experiment, 36 grass block are tested)
  Also if exposed to light level more than or equal to 12 and being adjacent to another grass block, a dirt should turn into grass block but after 3 in-game days no dirt was changed.

I don't think there's any need to give a picture as it is easy to reproduce this bug.