Your experience provides another reason for problems that a customer (and probably others) struck recently. The buyer was a US Ebay member residing in Japan. She was finding it impossible to accumulate multiple purchases, with the intention of then requesting combined shipping, as the sale would not complete unless payment was made (on each individual item). The items in this case were different colours of garment within a 'variations' enabled listing.

I don't know what device the buyer was using but it could well have been a mobile one. The Service Request reply that the buyer received from her approach to Ebay made no sense and it made obvious that the serviceperson was out of their depth over this matter.

The only solution is for the buyer to pay for all items including excessive individual postage trusting that the seller will honour the refund of this postage. I suspect that this is too big a leap of faith for many which could well result in the buyer going elsewhere, including outside of Ebay as was the case for us here.