Sales Invoice From Single Project With Multiple Timesheets

We have ERPNext v14.27.3. There are timesheets from two employees for various tasks in this project. When I choose to create a sales invoice for the project, I fill out the appropriate fields then I select the “Fetch Timesheet” button. No sale items get populated but all the timesheet entries are listed at the bottom with the total billed amount. When I choose to save the invoice, I get a balloon stating “Missing Fields - Mandatory fields required in Sales Invoice”. This shows the same blank items list. The documentation states an invoice can be created based upon timesheets just not this way apparently.

If I open the actual timesheet & choose the Create Sales Invoice button, it populates the invoice with the correct sales items but includes only the timesheet from one employee & not two.

How can I genearte a SINGLE invoice from timesheets for a project when there are timesheets from 2 or more employees working on a single project?