the more you are venturing out into the endless space, the more the selection got strange... off and snappy to strange points.
As you may see in both screenshots, 1st is far, 2nd ist way off and 3rd is don't ask... (you see in that case the coordiantes) the selection is by every step further away from the cursor. Also, the selection is not fitting to the grid anymore even with the distance, it's shifting between points in the grid, so that it's impossible to build on some points in the grid.
it reminds me big time of the Glitchworld bug, back then there was something similar with the item position vs. hitbox of the selector... So I assume it's something like that here as well.