How to override receivables credit tax

Hello,

We are trying to workout how to override the tax against an AR Credit. We have the following enabled:

1. Manage Taxes - Allow override of calculated tax lines and Allow entry of manual tax line
2. Manage Tax Statuses- Allow Tax Rate Override

When we go into Payables we are able to override the tax but in Receivables it won't let us. I've tried creating multiple AR invoices in the DEV system and even when I go into the specific line details and manage tax the tax rate etc is all locked.

If I raise an AR invoice however and do the above, I'm able to override the rate to be any % I'd like.