It seems like building placement is hyper, hyper sensitive and prone to many, many misplacements. For example, if I’m standing inside a 2x4 structure with walls and want to put a ceiling on, it’s almost impossible to place a floor up above. The blue building part will snap to the OUTSIDE of the wall; to put a ceiling on the inside, I need to run outside the structure so I can build on the opposite (interior) side.
If there’s already a matching structure adjacent (for example, building two floor panels side by side), it will usually snap into position. This doesn’t always work, though, especially with triangle pieces.
And try this on: Build a 2x4 shack of foundations and walls. Put a half block anywhere. Put a second row (second floor) of walls all around the perimeter, and notice how you can’t put a wall above the half block; it snaps halfway down as if to line up with the half block. You must demolish the half block before placing the wall. This is a big problem on stairwells.
Then there are times (usually when doing something like replacing an element that’s been destroyed or removed) when the blue part strobes in and out as you slowly move around. Placing something there will take a minute or two of experimenting with different placements, or sometimes demolishing the surrounding structure to at least a 2x2 hole and trying again.
I figured this would have been fixed in the last update, but it’s still in here, being as annoying as ever.