I also discovered last night that where you have a cross over between sea and land, ie
Land
Sea Sea
Land
Land units can cross it, but naval ones can't. I think it was different in CTP, but doing ti this way would make Skaggerack non-navigable, and also block the Aegean Sea from the Black Sea. What do you reckon I do for the Sea of Marmara (between Turkey and Europe, by Istanbul) - make it a land bridge or a water straight? I've made it water, though Kal-El did the opposite. It's not too hard for units to walk around, after all.