Bug in importing invoices

Quite nasty bug. When you have two or more invoices where subject is exactly the same, while importing such invoices from csv, system merging it and adding (doubling) line items! Spent half night to figure out what is wrong with importing invoices. To reproduce,

• create two or more invoices with the same subject
• export 'em to csv
• import 'em back or to other instance

In this case invoices has been duplicated to change value and old (with same subject) has been cancelled (status)