Classes on line items in cash sales/invoices?

Hi.  We recently enabled classes in our account, and checked the accounting preference that allows for per-line item classifications.  But the class option doesn't seem to be showing up in billing line items on transactions using the standard forms - cash sales, invoices, etc.  It does show up in the transaction header.  I tried customizing a form and that worked, but that means that to go through and add class information to all of our transactions, we'll have to first customize all of our forms - is that really necessary?

A related question - I assigned a class to a billable item in the Items menu, and then generated an invoice with it, not selecting a class in the invoice header or line item.  When I then run a report looking for transactions in that class, nothing shows up - shouldn't the class be assigned via the Item configuration, even if it's not assigned in the transaction itself?