Just tested this WITH the Open Sea Mod (after I got it to actually WORK) and it does it there too.BTW: I've been DirectSailing a bit today without the Open Sea Mod and it definitely IS still working weird-like.
After a reload to the next island, I tend to be almost right on top of it. And according the worldmap, I tend to be already PAST it.
The worldmap position seems to "fix" itself after a while.
Doesn't seem to do any harm though.