Java Version, Large Biome world
I noticed this bug in a world where I was messing around with the snapshot (in first screenshot), and after coming across this bug I promptly checked the bug tracker and tested it on a creative world.
If turtles are bred when all of the ground around them is taken, the egg placement gets weird. It seems to randomly decide where to put the eggs, instead of something like adding eggs to existing nests. It is not always near where the turtle is. If you look on the left of the sand box in the second picture, the turtles layed eggs through a wall when the floor had one layer of nests with one egg. Another later appeared.
In the first screenshot, you can see the survival world, where the turtles layed eggs outside of their "pen" (the sand and kelp box further away). It seems that it was placed there because it is closer in y-level to the turtle's position, but I don't fully know.
In the second screenshot, there is a box of sand, covered with one layer of turtle eggs, and when the turtles were bred, they would wait some time before digging, and eggs would be placed outside of the box.
I didn't see any other posts on this topic, although I don't doubt the possibility of there being one, but I figured a duplicate post is better than an unresolved bug. I hope this helps the aquatic update be released earlier, as I love the content so far!