Merged Invoices are displayed double on UI

Expected result: Merged Invoices Line Items should be displayed in one common Invoice, in SO# column should be displayed counter with tooltip, in tooltip related with merged Invoices SOs

Steps to reproduce:

1. on the Invoice list form go to the In Review bucket
2. check some Invoices
3. click Merge button
4. in the opened Invoice edit form click Save or Save and Approve buttons
5. check that displayed single common Invoice