Oceans have no ice even if they are situated near very cold biomes like "ice plains" or "cold taiga". F3 shows that these oceans are not "frozen ocean" biomes, they are default oceans. Close to unfrozed ocean I found a biome called "cold beach", it is covered with ice and it's normal. And I discovered that between the unfrozed ocean and cold biome's shore is a default river biome. Really? Why does river separate oceans from shores? I think unfrozen rivers are potential reasons of these biome-generation glitches...

World's seed:
-263424026
Coords:
x=-41520, z=2380