It seems I was mistaken when reading the wiki and didn't look closely enough at the .json hierarchy. Oops. My bad.
Can also confirm this affects entities like sand, concrete and gravel as well.
This issue can be replicated by using commands and teleporting around. It's inconsistent, but I was able to produce this a couple of times on my own without looking any of these up. Hope this issue can be fixed.
Edit: Does it have something to do with chunks? After reading more I realized it might be the distance I was flying and teleporting back. I would teleport myself to 0 256 0 and fly down. It was inconsistent because I would fly different distances every time.
Sonic, it was fixed in this weeks snapshot. It was still present even after the fix was supposedly applied many snaps back. Notice "Fix version(s)."
Also notice that this issue is already tagged as resolved and has been since 15w42a.
Of course it's already fixed in a future version; that would be the hope as this bug is well; game breaking. But that doesn't make the report invalid or need closing when they current (up until last week's snapshot) snapshots we're reporting bugs on have this bug.
If you don't want to get all these comments sent to you; I'm sure there's a way to unsubscribe from said alerts. It also might help if you let the topic die instead of commenting again.
This is issue is alive and well in all forms of transportation other than your feet and nether portals as I am aware. (15w50a) If you try to reload the chunks using the developer "F3+A" while riding a horse; it will not load any new chunks. Just those previously loaded. Chunks are loaded as soon as you step off of the Horse.
It was mentioned in another thread while I was looking for previous posts about this issue that when riding these entities; you're bound by their chunk updating(??)
I'm not major Java developer; but maybe switch it up so that when Horses/Pigs/Minecarts are in use by the player they're bound by the Player's chunk updating instead? Although I'm just speculating with no look at the code! Could be impossible.
Issue still persists in 1.14.3-pre3