Enderdragon's rotation incorrect when set while teleporting

I have a setup where an enderdragon is constantly teleported to the same coordinate, and I can turn on clocks to change his rotation. When I do this, however, his rotation is way different from any other mob I try this on. For example, when I set his horizontal rotation to 180 he faces south southeast, when he should be facing north (also the jump between 338.6 and 338.5 horizontal rotation is massive).