Problem with Coords Y

When I test something with tnt and when I blow up into the sky, I press F3 to see where I am and I press F5, I'm in Y 253, It's OK but after second I'm in 254 and up to 272 I see my body without textures and when I'm in 272, I'm fully invisible! And when I look up, I'm invisible, but when I look down, I see my body but without textures.. It's not very important but It's small bug...