I won bids on a couple of items that the seller had specifically said they will post together and have combined into one order under a single invoice, but they are now trying to charge full double the postage. They might just as well send them separately in that case!
Although the description was that they wouldn't 'discount' postage, the explicit offer to combine them led me to think that shipping costs for two in one package would be less than double. (I believe 'discount' would have been like another seller I often buy from who gives substantial reductions or free postage when several items are ordered. I wasn't expecting that.)

If the seller wasn't going to pass on the reduction in postage costs, why even mention sending items together?
I usually ask sellers before bidding if they combine postage, but the bit about posting them together led me to expect I'd just be paying a bit more, not double!
I only bid on the second item because it would be good value as an addition and presumed saving on postage for both seller and buyer. I can't cancel just that item now because the seller has combined them.