The situation is if a row is copied from one sheet to another, the Auto Number unique row ID coming from the source sheet will keep the same auto number on the target sheet. This results in duplicate Auto Numbers potentially, which causes duplicates in what should a column with unique values.
Yes! This is frustrating and confusing. Agree with Sam that we need an option though. Sometimes you need the original autonumber to copy, sometimes you want it to override. What would also help is being able to set more than one auto number column per sheet.