Confirmed in 1.16.1
Ok, a bit complicated but makes sense. Should have thought of that, thanks!
I just encountered this issue (1.15.2), and was completely lost as to why my commands weren't working before taking a deeper look into it. I set up five command blocks to teleport armor stands at one-block intervals along my sight. This screenshot was taken after having the command blocks teleport the stands along a line (wrongly starting at my feet), then running the exact command in the third command block (/execute at @p anchored eyes run tp @e[tag=3] ^ ^ ^3) which moved the middle stand up by about a block, where it should have been all along! (I also just tested with a funciton and in 1.6 pre-release 4 and had the same results)
Please take this bug seriously, as it is definitely messing things up for everyone!
no crash report because it have to kill it in task manager
I agree that this is useful, especially for custom dimensions. But they really need to fix it so it actually works as one would hope. I noticed that the border size resets in dimensions other than the Overworld when you relog, and it's somehow split into two distinct pieces:
The visible part, which mirrors the border in the Overworld and stops player movement as well as block placement.
And the invisible part, which can be altered by the /worldborder command, causes damage when you cross it, and also stops block placement.
The most dangerous part about this in my opinion is that a player could pass the invisible border without realizing, until they start taking damage and can't interact with blocks that is.