Merge Queries Scrambles existing data upon 'expanding rows'

Anonymous, 

Thanks for the reply, I managed to recreate this error in power bi,  how do I attach screenshots?

Basically I have a table of format Customer ID/Date/Details/Order ID. Based on Customer ID and Date I create an index using below formula, so that Customer orders are ranked from 1(oldest) to x: 

= Table.Group(#"Sorted Rows", {"Customer ID"}, {{"Count", each Table.AddIndexColumn(_,"Index", 1, 1) , type table}})

I then merge with another table based on Order ID (no duplicates, only unique values) and after 'Expanding Columns' the initial part of the table changes date order from newest to oldest and is re-ranked as such, the newest value being the rank 1 now.

Is it something related to buffering the table at some earlier point in the steps?

Thanks