I believe you just have a misunderstanding about what is happening. As explained above, the red ghost you are seeing is from frame 55. You do not have a key frame set on frame 55. You have key frames set on 50 and 60. When you change 60, I assure you that none of your other key frames are changed. Spine interpolates between your key frames (unless you set a stepped key), so the pose between key frames 50 and 60 are dependent on the keyed values at 50 and 60. When you change 60, the interpolation between 50 and 60 changes and this is why you are seeing the red ghost at frame 55 change.
For an example, say the key at frame 50 sets the rotation to 40 and the key at frame 60 sets the rotation to 100. If your graph has a linear curve (which is the default), then because frame 55 is halfway between keys 50 and 60, the rotation will also be halfway between the keyed values 40 and 100 = the rotation is 70. Now if you change the key at frame 60 to have a rotation of 120, then at frame 55 the rotation is halfway between the keyed values 40 and 120 = the rotation is 80.
I hope that clears things up a bit! :nerd: Depending on what you want to do, you can either set a key at 55 so that frame doesn't change when you change 60, or you can use a stepped curve.