Strange bug with spares invoices. On a small number of dealers, rarely, invoice sales are recording with deposit.  Cannot figure out the trigger or how to replicate this behaviour though I suspect for various reasons, that there are staff running invoices through in an unusual/obscure way which we've never anticipated or tested for.  This version includes additional guards to explicitly prevent recording of deposit on invoice sales.

Update : replicated behaviour. Staff are exiting out of complete screen after selecting invoice and then re-entering it. This is permitting them to key in a deposit amount. Now fixed this loophole.  Strictly speaking it is a legitimate usage pattern and it's usage at this time has no negative consequence (assuming the end user knows what they are doing) but I am deciding to remove it from c9 anyway in order to constrain and simplify system behaviour and because I suspect that in the case of one user at least: they don't know what they are doing and this is causing problems for them.