Two or more frames can occupy the same block by being attached to the sides of the surrounding blocks, pictures and frames can occupy the same block but more than one picture cannot occupy the same block, might not be a bug because pictures are block sized and are edge to edge and frames are not but thought I would add it on here anyway.
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I believe that frames were made so that multiple frames could be on one block
Frames are actually entities, not blocks, because they have behaviors that blocks cannot. Although this may seem weird, multiple entities are allowed to occupy the same block (such as a pig and a sheep in the same block). I believe that paintings are blocks, so entities can occupy a non-solid block, but other blocks cannot (for example, a minecart in tall grass).
Duplicate of MC-208