I was thinking the same as you mentioned but the interesting point is that the block 19 and the block 64 have no common position at all. One of them is as big as my level field and the other one as small as a stair. When you search for those blocks they get red so it shows you have selected them. One of the is small and the other one is way bigger that to be considered as a duplication of the first one.
That I asked what I should do. Is this a bug?