Let me help you with creating an invoice, batvalil. 

Every time you'll link billable expenses to an invoice, the details will always show on the invoice. 

As a workaround, you can create a separate invoice that's not linked to a bill. Though this option will create two different transactions, the bill, and the invoice. Also, this won't record a reimbursement to your expenses.

I can see how this option would be useful. I'll personally forward this feedback to our developers so they'll consider this and be part of the next update.

Reply to this thread if you have other concerns.