Is it correct to expect Non-Posting accounts (PE code = "N") to prevent quantities being entered?

I have configured a Job Master record and attached a Cost Break Down Structure with roll-up accounts. These roll-up accounts have Posting Edit Codes = "N" for non-posting. Then when entering Original Budgets (P510121) amounts can NOT be entered which I believe is correct and functions as I expect. However, my expectation is that Original Budgeted Units should also be prevented from allowing entry against the account with Posting Edit Code = "N". I am finding that this is not the case. I have researched the Project Costing online manuals for any documentation around this but found nothing specific as