Some thoughts are AngryJoe's HOIIV preview

[podcat]

We tweaked down plane amounts last week. Ships can still cross over land parts tho

Johan mentioned in one of the MP streams about ships clipping land and looking at reducing their size or something to that nature but I think you can still assign just one sea province instead of all three.

you can get the problem with single zones as well so its actually a bit harder to fix than just that. it needs to pre-check paths and not route the ship animation where there is a land midpoint etc.
Graphical glitches that dont affect gameplay always get lower priority than gameplay tho, but we'll get there.