When you place redstone, fences, pistons and other blocks which don't fill the whole clock of air. Redstone takes up a whole block, and sometimes even two blocks. Fences hitboxes are very bugged, and sometimes even non-existent. The extended part of a piston's arm takes up 3/4 of a block. See attachments for all example shown, besides fences. We originally though this to be a bug with the plugins we had installed, but we recently went to 1.5, with bukkit not installed, and the same bugs are happening. All times this has happened have been at high coordinates, and never at low coordinates, such as near spawn. We believe this can be re-created by going to high coordinates and using the bugged items.