Can no longer create a contribution with a negative amount - a regression as in 4.4 this was ok

In 4.4 LTS:
add a -$1 contribution - save - done

In 4.6:
add a -$1 contribution - save [no errors]
you end up with a $0 contribution

Negative contributions have always been a solid and flexible pathway to record refunds and partial refunds (for event tickets e.g.) and I know many/large projects use this extensively at the direction of their Accountants/Bookkeepers, because refunds and partial refunds have their own transaction dates [at times spanning months/statements] and their own transaction IDs from Payment Processors - they are separate processes/transactions for reconciliation purposes. If you get a (partial) refund in a store - a week from your original purchase - you will have two contributions on your credit card/bank statement: one for the original purchase - and one for the (partial) refund.