This is something that has always been annoying to me as well.
What happens is, once you perform an auto-completion, SublimeText allows you to "tab" through to the other fields.
This is actually very useful, but there is one problem:
If you decide you don't want to tab through the fields (cause you moved your cursor away, for example), the fields are still there. The next time you hit "tab", it will go back to the fields you left out.
What you can do right now
First of all, you should try and actually use the tab to go through the fields. This is oftentimes convenient.
Secondly, notice that down in the statusbar (at the bottom of the screen), it says "field 1 of 4". Whenever you see that and don't want to use tab to go through the fields, just hit the "Escape" key, which will cancel the behavior.
Long term solution
I think the way Sublime should behave is like most other editors in this case. I'm pretty sure what they do is that, as soon as you move your cursor with the arrow keys, it cancels the fields. It's also possible that they only cancel the extra fields when you move the arrow keys away from the line itself, not just any movement.