So I was exploring the world when I found a piece of gravel that was rendered as an item. Wut? I thought it would be rendered as a block? And btw, YES, I DID check to see if there were any duplicates, and there doesn't seem to be any, so this is an original issue.
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Can you create a new world with the same seed and reproduce this? Like /tp to the same location?
No, I didn't drop it, or anyone else, I just found it there lying on the ground. Honest!

Please provide seed and location so that the case could be reproduced.
The seed is 5886968174052442556 and the locations is x: minus 21866873, y: 64, z: minus 1979286. Hope I Helped! 😃

Alas, I only found ocean at those coordinates with the seed. Tried both default and large biomes.
However, the coordinates are quite large, there is a good chance that the issue is caused by floating-point errors, which start to have various effects already at x/z +/-500,000 (according to http://www.minecraftwiki.net/wiki/Far_lands). And the given coordinates are well beyond that.
Resolving as duplicate of MC-3718.
What? NO! For a second I thought I had reported an original issue.... X( How am I EVER going to find a glitch no-one has discovered before? T_T My job as a glitch hunter is not going well........

Just a confirmation: I managed to spot couple examples of this issue, too. But, as expected, at very large coordinates, around 17,000,000 and 17,000,000. So, I'd say the large coordinates is indeed the common factor. I'd guess some calculation related to falling gravel (or another reason to create gravel item) does its job at floating-point world-coordinates and gets the location wrong due to floating-point math inaccuracies.
For the record, seed was -753548930 (normal), moving around the jungle near those coordinates. Within couple minutes I noticed two gravel items, the other was near coords x 17,000,053 y 16,999,907. Of course, the gravel items will be gone soon enough.
Maybe I'm missing something, but...
Hold gravel in hand
Press Q
Profit?

Yep, you're missing the point that no holding gravel in hand and/or pressing Q was needed; the seen gravel items were created by world generation, in places where there is no gravel anywhere near (except perhaps underground). Thus, the effect of seeing such gravel items is a bug. However, due to the very likely cause being the large coordinates, this is considered duplicate of that MC-3718.
Sometimes the world generation can create floating gravel blocks, which will wall down. And then sometimes they fall on/in some blocks and try to become a block, but because at that position there is already a block, they will drop.
But on the screenshot it appears as it was dropped there by someone. You could have dropped it accidently, or is this on a multiplayer server? Because then another player could have dropped it.