NO this DOES NOT WORK! I have read this entire thread to hopefully find a solution at the end. I don't know how many times people have suggested changing the name to the "project" under the customer name and, bingo! NO NO NO this does not work. LINKED TRANSACTIONS will be deleted when trying to change a paid invoice. I am no engineer but this seems a little ridiculous that this has not been fixed. It has been a year. I really wish I had known this before upgrading QB for the "projects" feature. I have all my Expenses (job supplies, subcontractors, etc) under the specific project. BUT ALL my projects I have no profits because I CANNOT LINK A PAID INVOICE TO THE PROJECT. This is the issue. This projects tab is worthless to me until this can be fixed. 

So please fix this issue!