In Minecraft 1.4 (Windows 10 Edition), when I transport a cat in a boat over larger bodys of water (deep rivers, oceans), after a few moments the cat (no matter if kitten or adult) starts to receive continuous damage until it dies.
PS: I discovered, that the SAME bug also applies to RABBITS.
I can repro this in Windows 10/Bedrock 1.4.2
Cat in boat - continuous damage and it dies within a few moments.