Billing block is hidden when required fields not otherwise available

We have a complaint from a customer that they collect 'postcode' on their profile. Because this is one of the billing fields the 'billing address is same as above is added'. The billing fields are hidden and people don't realise they need to fill in other compulsory billing fields and wind up getting validation errors on form submit.

I think that the hiding part of the above is new since 4.2 which they recently upgraded from.

My suggestion is that either the billing block is only hidden if ALL the compulsory fields are elsewhere on the form or it is only hidden if all the compulsory fields in the billing block are populated (ie. it would be hidden on the fly once the fields are populated). Note sure which is better of these two. Perhaps the second would be confusing - ie. it would imply that it would 'disappear' once you fill the last required field.