Spine always choses the closest direction when rotating. So for example if you need to rotate 360 degrees create 3 keys at 120 degrees.
Unfortunately this makes it more difficult to use the graph.
We could correct this quite easily in Spine I believe. The problem arises at runtime where some toolkits might not support < 0 degrees or > 360 degrees of rotation.
I know it's something we will look into changing, but I can't say when it will happen.