Hi Sven, thanks for answering. Yes, I've tried to create it from the analytic journal items, and it still creates 2 separate invoices: one with the hours, the other with the expenses.

Do you know of an existing custom module that adds the invoice option for both hours and expenses? Or, do you know something similar I could use as a starting point to design my own?

edit:

yes, I confirm that only one analytic account was being used for both time and expenses. Not sure which build I have of odoo8, and have not used runbot before. Will follow up and see what happens. Thanks for the tip. If you think of anything else please let me know.

edit2:

You're right. Testing on runbot, the latest version of Odoo8 creates one invoice, not two. Now I need to find out if I have a setting wrong, or if I need to update my version of Odoo.

edit3:

Bad news. I updated my install of Odoo with "git fetch && git reset --hard origin/8.0", and checked that some of the files in my installation were updated to today's date. Then tried creating the invoice again. Still getting two invoices: one for hours, and another for purchases from purchase order. Any ideas?

edit4:

OK, so I forgot to restart Odoo after doing the git reset. After restarting, it now works fine. Must have been something fixed in the latest versions. Thanks for your help.