phantom "Pending refund" status after price set change?

We use direct debit (civisepa) as a payment processor, which of course is a sort of pay later payment-processor, until we send the payments that are due to the bank.

Now we have a situation I think is a quirck in the partial-payments system.
1. A customer registered for an event using a price-set. Total sum: 150 euro
(event registration and contribution get correctly recorded as pending)
2. The next day the customer emails and says she does need one of the items in the price set.
3. I change the payment, deselect the price set item.

What happens next is unexpected behaviour
a. The amount in the contribution changes correctly to the new total amount (total sum: 140 euro)
b. the contribution status changes to 'pending refund' (a refund of 140 euro?)
c. I cannot change the status back to 'pending'

It is the last part that is a problem for us. When handling direct-debit payments, contributions with status pending should keep their status after a price-set change.

A solution would probably be to handle direct-debit payments for events in the following way:
1. direct debit payments that directly transfer to a payment provider get the status 'progress'.
2. direct debit payments that mannually ge processed get the status 'pending'. This status needs to change to 'progress' when submitted to the bank.

Any help or wisdom on this suggestion or my orginal problem?
The fact that the contribution gets the sum 140 and status 'pending refund' seems to be a bug, doesn;t it? If I wouldnt have noticed it we would have lost the contribution or refunded a huge amount in error.