I believe one of the reasons for this is because of the new 1.13 water physics. Water can now flow over more blocks than it was able to in previous versions. For example it can now flow over slabs, stairs, trapdoors and so on. So when it comes the plots, the borders are made of slabs. So people could use it to spill water everywhere are make a big mess.
However the tics being off, makes sense too.