The Union Jack is actually defined by the ratios of the lines constructing it, rather than being a set design printed at various sizes. The two most common size ratios are 1:2 and 3:5, with 1:2 being used in official capacities and 3:5 generally being flown on land otherwise. When printed at a 3:5 ratio the design changes slightly due to the corners being positioned differently relative to each other, so the diagonals become steeper and the corners of the bottom left and top right diagonals get cut off.

Afaik it’s the only flag with a design that causes this to happen when printed at different size ratios.