Sounds like you need to hire more proficient engineers.  How long does it take a group of developers to isolate a bug in a software feature that once was perfectly functional?  The only information we ever get from Quickbooks in regards to this issue is a generic message telling us to "rest assured" that engineers are tackling the problem.

The ability to issue customized invoices which REMAIN LINKED to original estimates is a foundational component of business sales operations and is an integral feature for which we pay Quickbooks.  If this feature continues to remain unavailable for such an extended period of time, Quickbooks should make good with their currently subscribed members and offer a monthly discount.  There IS NOT a fully satisfactory workaround to this issue and it's been months since it was originally reported.  

Come on Quickbooks!