Tried building a ship. Tried replacing some internal Systems but found that I was unable to remove these internal blocks.
1) Spawn any ship, or make a ship core, and make say, a 10x10x10 cube of blocks with build mode.
2) While still in Build Mode, Try to remove central blocks from this cube, or from internal system areas of ship, with the camera inside the vessel by at least 1-2 blocks
3) Notice inability to remove blocks in front of you while "inside" the ship blocks in build mode
This is also true for Advanced build mode