I use this portal a lot when ordering online. I'd say nearly 40-50% of transactions made through Mr Porter end up being reversed. It took me a while to realise that any item you return within a Mr Porter transaction means they just cancel the entire transaction. So if you order 5 items and send back the cheapest item, you end up losing all the points gained. Mr Porter is supposed to recalculate the transaction, and then resubmit the new amount, but never does. It's just reversed.

I opened a case, they told me Mr Porter is responsible for the allocation of points and you need to speak to them. So eventually found the person at Mr Porter who handles this only for them to tell me to speak with BA Avios and that they simply report back transactions and whether they are cancelled or not. Basically - both blaming each other. My guess is, the person who handles this at Mr Porter voids any transaction refunded, whether it's the entire amount or part of it: job done, move on. No-one cares enough about it.