Blocks of the world will be rendered inside the view-distance-border-region (one chunk wide) when:

1. Blocks are built above Y=240
2. The Viewport (Eye-Height) of the player is above 256

This only happens (in singleplayer) if the blocks area inside the 1-chunk border that is loaded but not visible.

The attached screenshots show this problem.

First screenshot:

• The blocks are within the set view distance and everything is visible as expected

Second screenshot:

• The blocks below 240 are unloaded as expected
• The blocks above 240 are still visible outside of the set view distance

The problem exists in 1.15.1 singleplayer and 1.15.1 server. Setting the worldtime to /time set 13000 helps spotting these problems.