That's confusing to me. Swapping 9,10 should make a difference, without changing the code. One way is right, one way is wrong. It may not affect your total count, as you have observed, but it will not step in the right order, individual steps I mean. This could lead to...
Skipping, ahead, not behind.
You don't have to go THAT slow. It takes too much time to do an experiment at that speed.
What surprises me is that you're so close to being correct. I have seen a similar closeness when starting full speed and stopping without gradual accell. It only misses a few steps at the beginning. You case is different. I don't understand your symptoms. Try going at your speed of 1 and see if it takes tiny steps, equal size, equal time, all in the same direction. Not jerky or uneven.