I was saying my license plate number to someone the other day, and when the clerk repeated it back to me, she used Sino-Korean numbers for everything (as I would expect) except she said 하나 (native Korean) for the last number. For example, if my license plate number was something like "34라1891", she would have said it as "삼 사 라 일 팔 구 하나". Note how the first one is pronounced as 일, but the last one is 하나.
I asked a Korean, and was told that this was common for final 1 digits in colloquial Korean, but it left me with a few questions. Does this only apply to 1 or other numbers too? Where did this twist come from? Is there any rule for when or how to use this?