@Markro, update your software. Several changes to the way Billable Expenses work were made since your version. The Guides will not make sense with your version of the program. Read about the new processes in these Guides:
As for your issue with quantities and prices, @Brucanna was on the right track, but you made it impossible to answer completely, because your initial post did not mention Billable Expenses. When you post a purchase to the Billable expenses account for a customer, you are not buying it for your use or inventory. Instead, you are purchasing it for your customer. The only place it initially appears is in the Billable expenses asset account. When you invoice the billable expense, you are not transferring quantities and prices to Accounts receivable, but only the amount. So all description of the amount must go into the
Description field. This is what prevents you from invoicing the customer for items from your own inventory or other things you own.
Your question, however, revealed a bug with multi-line payments posted to Billable expenses. I will write a separate bug report about that.